# Depth of field (DOF) does NOT change with sensor size



## donny1963 (Nov 18, 2018)

here is another BS statement i hear all the time and just watched Ken explain this in a video..
Dept of field does not change with sensor size. 

If you take a 50mm lens and attach it to a Crop sensor camera then also that saame lens then  attach it to a Full Frame or Even Medium format camera and your standing in the same postion the DOF will not change they will all be the same.. When people say sure it changes, i laugh and think to myself these are the same people who argue that larger sensors gather more light. Which is not true either..

Sensors do not work like solar panels LOL

any way here is the video explaining all this about  Depth of field (DOF) does NOT change with sensor size


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## Tim Tucker 2 (Nov 18, 2018)

That's what equivalence does for you...

Although having a TAP video makes me want to run away, as quickly as possible, you have to fully understand the the relationships between sensor size, DOF, fov, focal length and exposure.

These are so intrinsically linked that if you change one then another will change by a proportional amount, and if you hold certain parameters constant then others will stay constant.

For instance if you adjust aperture then exposure changes unless you make an equal change in shutter speed where it doesn't.

The thing is that *if* you hold the total amount of light falling on a sensor and fov as constant then DOF is also constant but exposure changes, if you take *equivalent* shots with different sensors in that the total amount of light and the fov is equal in both shots then both will also have the same DOF but _they will have different exposures_. If you hold exposure constant then the *equivalent* shots will have different DOFs.

The thing is that by stipulating the conditions in which to compare the noise characteristics of different sensors then you have to set conditions to cancel out differences between them. In other words you stipulate that comparable photos must have the same total light and fov then they *must* also have the same DOF. It is then a little silly to state that DOF if the same between all sensors when you first set the parameters so it must be.

Basically by cancelling out sensor size you also cancel out focal length, but then exposure must vary between *equivalent* shots because you deal in actual aperture diameter instead of f-stop. If exposure is constant then DOF varies because you deal with f-stop which is proportional to focal length.

The calculations are over-simplified and are not fully correct anyway. The system works and allows you a different understanding of the relationships, but only if the relationships remain proportional. DOF is only proportional at portrait distances but not at landscape distances. It only changes in a proportional manner up to the point where infinity is said to be within the DOF, (hyper-focal distance to infinity), then decreasing aperture only increases DOF towards the camera, and it is no longer proportional to aperture.  This allows you to take landscape images with smaller sensors that have essentially the same DOF without *equivalent* settings. The system doesn't fully explain these relationships, it is just a special case that only exists in theory and only exists because you stipulate as a condition of proving it that it must, (_lens performance is linked to f-stop rather than aperture diameter and therefore focal length can't be cancelled from the equation because we arrive at the situation where an aberration loaded image at f1.4 is equivalent to one shot at f4, by proving focal length is irrelevant we must first ignore where it is relevant_).

I find that it does allow you a more complete understanding of the relationships between the fundamental controls of the camera, but is also used as a sort of *geek speak* by those who want to create the illusion that they understand photography and digital better than anybody else, rather than my preferred method of using understanding to create better images. It becomes a sort of elitist club with silly handshakes and jargon...


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## Overread (Nov 18, 2018)

If depth of field doesn't change with sensor size why is it when I compare medium format photos to mobile phone photos the depths of field are VASTLY different even at the same settings?

Also why would most (if not nearly all) calculations for depth of field require sensor size in the equation if it has no effect. Since sensor/film size affects the circle of confusion value


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## Vtec44 (Nov 18, 2018)

Tim Tucker 2 said:


> I find that it does allow you a more complete understanding of the relationships between the fundamental controls of the camera, but is also used as a sort of *geek speak* by those who want to create the illusion that they understand photography and digital better than anybody else, rather than my preferred method of using understanding to create better images. It becomes a sort of elitist club with silly handshakes and jargon...



Pretty much...  

I mean understanding the technology is great but how do you put it in practical uses, in this case create beautiful images?  In many cases, there are numerous people who are great at repeating the information but have no real knowledge practical application of the technology.  I'm not referring to anyone in particular just a general observation.


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## petrochemist (Nov 18, 2018)

The amount of blur on the sensor doesn't change, but AFAIK no one actually views their pictures directly on the sensor. When you output images from small sensors you magnify them more so even without changing position or focal length DOF will change.
It also changes depending on how the images are viewed so the simplistic calculators that use a fixed circle of confusion for each sensor are not a great deal of help if they're not set up using the conditions your prints are viewed at. Pixel peepers need much sharper images (smaller coc) than those downsizing for the web or making the old 6x4 size prints.


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## Tim Tucker 2 (Nov 18, 2018)

Vtec44 said:


> Pretty much...
> 
> I mean understanding the technology is great but how do you put it in practical uses, in this case create beautiful images?  In many cases, there are numerous people who are great at repeating the information but have no real knowledge practical application of the technology.  I'm not referring to anyone in particular just a general observation.



LOL, yes indeed. Especially:



Vtec44 said:


> repeating the information



This highlights the basic contradiction and mindset I've always had a problem with and have never been able to communicate to *equivalentoligists*. That the act of producing equivalent photographs requires you to have a reference point of another photograph to be equivalent to. Basically it's the science of being able to copy not create.


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## Tim Tucker 2 (Nov 18, 2018)

LOL, now having watched the video because a little light entertainment is always good on a Sunday morning, I am now in a more jovial mood.

There are so many basic mis-conceptions and mistakes, that the amount of hysterical laughing and giggling are about the only relevant things in the video. By rubbishing others and ridiculing viewers for blindly following what they say he is quite categorically asking you to do the same here. It's a complete waste of time.

Images are our human perception of them when we view the *finished* print. The idea that they are fixed on a sensor by the action of a lens and that if a lens is the same then the image therefore *must also be* is completely false. There are so many things that are different, (fov, magnification etc...), that the only logical conclusion is that your perception of the finished image must be different, not the same.


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## AlanKlein (Nov 18, 2018)

I put this example (2x crop sensor) together to explain it to me a few years ago.  To me it seems that the smaller sensor (2x crop sensor) acts like a telephoto lens capturing a smaller part of the picture, half the FF sensor would do.  That decreases the depth of field just like doubling the lens would do on a FF camera sensor.  If you halved the lens to a wide angle, the DOF would be the same.


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## Ysarex (Nov 18, 2018)

donny1963 said:


> here is another BS statement i hear all the time and just watched Ken explain this in a video..
> Dept of field does not change with sensor size.
> 
> If you take a 50mm lens and attach it to a Crop sensor camera then also that saame lens then  attach it to a Full Frame or Even Medium format camera and your standing in the same postion the DOF will not change they will all be the same..



Wrong.

Proof:





(Just for the sake of maintaining some semblance of rationality, LOL, assume the lens above is a Hassleblad 50mm Distagon.)



donny1963 said:


> When people say sure it changes, i laugh and think to myself these are the same people who argue that larger sensors gather more light. Which is not true either..



Wrong.

You are confusing exposure with light gathered. You made that mistake earlier and were corrected: So Who Believes that Full Frame Camera's Gather More Light Then APSC




donny1963 said:


> Sensors do not work like solar panels LOL
> 
> any way here is the video explaining all this about  Depth of field (DOF) does NOT change with sensor size



A blathering idiot.

Joe


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## Ysarex (Nov 18, 2018)

Tim Tucker 2 said:


> LOL, now having watched the video because a little light entertainment is always good on a Sunday morning, I am now in a more jovial mood.
> 
> There are so many basic mis-conceptions and mistakes, that the amount of hysterical laughing and giggling are about the only relevant things in the video. By rubbishing others and ridiculing viewers for blindly following what they say he is quite categorically asking you to do the same here. It's a complete waste of time.
> 
> Images are our human perception of them when we view the *finished* print. The idea that they are fixed on a sensor by the action of a lens and that if a lens is the same then the image therefore *must also be* is completely false. There are so many things that are different, (fov, magnification etc...), that the only logical conclusion is that your perception of the finished image must be different, not the same.



I'd suggest saving it for late some Saturday night and start drinking before you start the video as it's not very long.

Joe


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## Braineack (Nov 18, 2018)

[





donny1963 said:


> If you take a 50mm lens and attach it to a Crop sensor camera then also that saame lens then attach it to a Full Frame or Even Medium format camera and your standing in the same postion the DOF will not change they will all be the same.. When people say sure it changes, i laugh and think to myself these are the same people who argue that larger sensors gather more light. Which is not true either..



Go outside, actually do this test, and then see if you keep laughing...

you literally have not done this test yourself, and do not understand the science behind it, yet youll sit here and laugh at the people who actually understand and know why the DOF does change.

SAD.


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## Braineack (Nov 18, 2018)

Ysarex said:


> A blathering idiot.
> 
> Joe




you left out a few choice adjectives.


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## donny1963 (Nov 18, 2018)

petrochemist said:


> The amount of blur on the sensor doesn't change, but AFAIK no one actually views their pictures directly on the sensor. When you output images from small sensors you magnify them more so even without changing position or focal length DOF will change.
> It also changes depending on how the images are viewed so the simplistic calculators that use a fixed circle of confusion for each sensor are not a great deal of help if they're not set up using the conditions your prints are viewed at. Pixel peepers need much sharper images (smaller coc) than those downsizing for the web or making the old 6x4 size prints.



the dept of field doesn't change, how ever the crop does change, that's the only thing the DOF does not change at all.. unless you use a different lens..

Donny


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## Ysarex (Nov 18, 2018)

donny1963 said:


> petrochemist said:
> 
> 
> > The amount of blur on the sensor doesn't change, but AFAIK no one actually views their pictures directly on the sensor. When you output images from small sensors you magnify them more so even without changing position or focal length DOF will change.
> ...



Wrong.

Proof:



 

Joe



donny1963 said:


> Donny


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## donny1963 (Nov 18, 2018)

Ysarex said:


> donny1963 said:
> 
> 
> > petrochemist said:
> ...


First of all your comparing Digital to actual film..

full frame or med format vs crop sensor doesn't matter  DOF will not change.. Just because of Sensor Size..
NOPE!!!!!!!


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## donny1963 (Nov 18, 2018)

every lens made on earth craps out the same light same bokah same everything regardless of what sensor it is used on.
a 50 mm lens will output the same thing on a crop sensor vs a full frame or med format camera..
same everything nothing changes.. except the CROP!!!!! smaller sensors that same lens will zoom in a bit according to the crop, but WILL NOT CHANGE THE DOF!!!!
the only time the DOF will change is if you step back to get the same focal length on the crop sensor vs you doing it on a full frame sensor that is the only way DOF WILL CHANGE,
you would have to change your distance to the subject that would change the DOF but it's not the Sensor that changes it, if your in the same exact position taking the shot on larger sensors vs smaller sensors the DOF WILL NOT CHANGE!!!
that is an undeniable fact period!!!!
now matter how you slice it... SORRY, but many people are under the illusion that DOF changes but, fact is it doesn't just like larger sensors do not gather more light then crop sensors.
this is another misconception fallacy that people think larger sensors gather more light, NO they don't, they are not solar panels they don't work the same as solar panels..
OMG!!!!!!!!!!!!!!!!!!!!!!!!


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## Ysarex (Nov 18, 2018)

donny1963 said:


> Ysarex said:
> 
> 
> > donny1963 said:
> ...



Digital/film makes no difference and after all it was you who started this thread with "If you take a 50mm lens and attach it to a Crop sensor camera then also that saame lens then attach it to a Full Frame or *Even Medium format camera*..."



donny1963 said:


> full frame or med format vs crop sensor doesn't matter  DOF will not change.. Just because of Sensor Size..



Wrong.

Proof:






Joe



donny1963 said:


> NOPE!!!!!!!


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## Ysarex (Nov 18, 2018)

donny1963 said:


> every lens made on earth craps out the same light same bokah same everything regardless of what sensor it is used on.
> a 50 mm lens will output the same thing on a crop sensor vs a full frame or med format camera..
> same everything nothing changes.. except the CROP!!!!! smaller sensors that same lens will zoom in a bit according to the crop, but WILL NOT CHANGE THE DOF!!!!
> the only time the DOF will change is if you step back to get the same focal length on the crop sensor vs you doing it on a full frame sensor that is the only way DOF WILL CHANGE,
> ...



If you repeat wrong and add a bunch of !!!!!!!!!!!!!!!!!! you have wrong!!!!!!!!!!!!!

Proof:





Joe


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## smoke665 (Nov 18, 2018)

Here we go again


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## Ysarex (Nov 18, 2018)

smoke665 said:


> Here we go again
> View attachment 166048



This should be a pretty short one. It is regrettably worth the effort because Mr. Apophasis and Donny are not the only proponents of this fallacy and so getting the public record straight has value for novices who might otherwise stumble upon the nonsense and be persuaded.

Joe


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## Tim Tucker 2 (Nov 18, 2018)

Slow down, chill out and reflect, rather than jump to conclusions - observe.



donny1963 said:


> the only time the DOF will change is if you step back to get the same focal length on the crop sensor vs you doing it on a full frame sensor



So focal length changes with camera position? I'm sure you don't mean this, but the just same in the video TAP spews out a misconception and expects you to accept it as fact without thinking.



donny1963 said:


> you would have to change your distance to the subject that would change the DOF but it's not the Sensor that changes it, if your in the same exact position taking the shot on larger sensors vs smaller sensors the DOF WILL NOT CHANGE!!!



No, changing your distance to the subject changes your point of focus.



donny1963 said:


> that is an undeniable fact period!!!!



Or misunderstanding presented as fact for Youtube traffic? Don't forget the amount of hysterical laughter in the video, it's relevant. Especially the bit about equalising fov by changing camera position...



donny1963 said:


> SORRY, but many people are under the illusion that DOF changes but, fact is it doesn't just like larger sensors do not gather more light then crop sensors.
> this is another misconception fallacy that people think larger sensors gather more light, NO they don't, they are not solar panels they don't work the same as solar panels..
> OMG!!!!!!!!!!!!!!!!!!!!!!!!



So what did the photo look like? I mean have you actually used this to understand and take an image, communicate a thought through the taking of an image? Has it ever even influenced how you focus, compose or expose an image? Is it actually possible to use any of this to create an image? Have you ever seen this in an image, tried to confirm this by taking images?

TAP creates confusion and mis-understanding. None of what he spews makes any sense at all, and above it all is the voice that says "believe me without question, it is truth!" The whole history of photography and the relevance of the images has not suddenly collapsed because of his revelations. That so many images have been taken that are relevant and thought provoking in the pre-TAP era and continue to be taken by those who consider him a blithering idiot kinda indicates his relevance...


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## WayneF (Nov 18, 2018)

That was a really dumb video, which was totally incompetent to discuss its subject.  It was embarrassing to watch, I couldn't make it past half way.  No redeeming merit whatsoever.  My concern is that some newbie will see it and suffer a setback with wrong information.

It is true that the image that  a lens does output does not depend on the sensor. A lens does what it does. But we don't view that direct lens image, and that is simply NOT what Depth of Field is.

Depth of field is about *viewing enlargement*, how much we enlarge that lens image until we can actually see that focus blur that the lens might do.  We enlarge the original small sensor size or film size into a larger view that we can actually see, to be able to see and judge the focus blur.

Depth of Field is computed from Circle of Confusion (CoC), which is the diameter of that blur spot from the lens.  In practice, DOF specifies the term CoC as an acceptable maximum limit of that diameter.  The blur diameter is of course seen better when we enlarge it,  and which is even overlooked if kept too tiny to see. Depth of Field is about seeing the blur.

CoC is numerically computed as a divisor of the sensor diagonal (typically CoC = diagonal/1442 or sometimes /1500).    Because, the smaller the sensor, the more its image has to be enlarged to view it.  And the more we enlarge it, the better the blur shows up, and becomes more objectionable (and we don't like objectionable).  The lens does what it does, but Depth of Field is about the enlargement we use to view it.  We see detail better in greater enlargement sizes. The blur spot is much larger on the enlarged print or monitor than it was coming out of the lens.  And thus more objectionable, so enlargement of the small sensor is a very important criteria.

And in fact, the standard Depth of Field is computed from the enlargement of that small sensor size to (by standard definition)* to an 8x10 inch print viewed at 10 inches*.  Numbers vary slightly, depending on source, but for example, full frame 35 mm cameras typically use CoC of 0.03 mm (43.267 mm diagonal / 1442 = 0.03 mm CoC),  that being the maximum acceptable blur spot size from the lens onto the sensor, which when then enlarged to standard 8x10 inch print size, becomes about the limit of what the human eye can see, which is when larger becomes important.

Specifically, DOF computes limits at the distances where the blur diameter exceeds this CoC limit, meaning when it could be seen by eye when sensor size is enlarged to 8x10.  The lens focuses at only one distance, and it does what it does elsewhere, which becomes blur when enlarged enough that we can see it, but is not considered blur if we can't see it.  Coc, and thus *Depth of Field depends on enlargement, which of course depends on sensor size.  *If viewing smaller than 8x10 inch inch size, then DOF will be better than computed, which is not often a problem. But if viewing larger than 8x10, DOF will be worse than computed.

Smaller sensors (a few mm size) have to be enlarged much more to reach an 8x10 inch print, so their allowable CoC that we must compute with is much smaller. (Fortunately, their  cropped field of view has to use a much shorter lens, which is less magnification from the lens, which more than compensates in the DOF formula.)  The computational tool is that their sensor diagonal is much smaller, so diagonal / 1442 is much smaller CoC, for that reason.  Every existing DOF calculator is computing this enlargement of CoC, which depends on Sensor size.

Depth of Field is a very worthy subject to discuss, but try to forget that embarrassing video. Try to forget you ever heard of it. Apparently just some guy seeking Youtube views with ridiculous claims.  A lack of understanding, blatantly wrong.


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## Derrel (Nov 18, 2018)

The Angry Photographer's videos are for entertainment purposes only, and no valid technical information should be be expected from them. Users should watch his videos at their own risk. Opinions expressed in TAP videos are the property of The Angry Photographer, and do not necessarily reflect the opinions of people who actually understand photography fundamentals.


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## WayneF (Nov 18, 2018)

I suppose I've lead a sheltered life, as I had never heard of him.      Some people must have strange notions about what they think is funny, but I think we should try to help the newbies to understand photography.


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## Dave442 (Nov 19, 2018)

Great point bringing up CoC. The DOF estimations and F-stops make are great developments that allow photographer to focus more on the art of photograpy. 

Any discussions about the physics of DOF or Total light gathered have to include all the variables used in said calculations (such as CoC, actual aperture diameter, etc).


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## Overread (Nov 19, 2018)

First, great post Wayne and thanks for giving a far more detailed reply  



WayneF said:


> I suppose I've lead a sheltered life, as I had never heard of him.      Some people must have strange notions about what they think is funny, but I think we should try to help the newbies to understand photography.





Every market has them. Though I don't tend to lurk enough photography youtube pages to know them, but in the Computer game world there are some that can rise to have quite large and extensive fanbases. Some are very snide and hostile with their commentary, whilst others are clearly playing and acting it up and their attitude is more jovial and less hostile. However the core element is the same in that their videos tend to point out problems (real, imagined or based on personal interpretation) and then deride and insult other groups.

Those watching get entertainment and some a sense of superiority because they are agreeing with (or being ledby) the the video host in being superior to those who are being insulted in the video.

Of course those making the videos often realise that they can get a huge market by publishing "bad news" or extreme viewpoints (good old Ken Rockwell was very much like this, only his views were more just personal preferences and often presented as such. Ergo he was extreme, but rather tame and not confrontational/hostile. Heck when he became popular many other reviewers poked the joke back such as commenting on how they used a tripod even if Ken God Rockwell didn't


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## Braineack (Nov 19, 2018)

donny1963 said:


> every lens made on earth craps out the same light same bokah same everything regardless of what sensor it is used on.
> a 50 mm lens will output the same thing on a crop sensor vs a full frame or med format camera..
> same everything nothing changes.. except the CROP!!!!! smaller sensors that same lens will zoom in a bit according to the crop, but WILL NOT CHANGE THE DOF!!!!
> the only time the DOF will change is if you step back to get the same focal length on the crop sensor vs you doing it on a full frame sensor that is the only way DOF WILL CHANGE,
> ...



So I take it you couldn't be bothered to go test it yourself?


Would you believe B&H?

Depth of Field, Part III: The Myths

they even show the math and examples...  [there's also a video, but the girl doesn't just tell and actually explains things, so you might not be able to follow along.]

and just because I know you won't be bothered to actually click the link and learn:





_borrowed from the above link._



> So, at 5.9' and an aperture of f/2.8, there is a 2.9" difference in the total DOF for the two different sensors (almost 1.5" on the near and far side). The APS-C camera has a shorter DOF when using the same lens at the same aperture and distance.




not shockingly [for us, not you], the 50mm Crop vs FF shot, the DOF is completely different and the crop sensor has much better background blur as result.  You can clearly see the crop sensor shot is NOT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! the same image as the FF just cropped in -- you can see the crop sensor is doing a better job of blurring out the metal fence posts here.


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## WayneF (Nov 19, 2018)

Overread said:


> Of course those making the videos often realise that they can get a huge market by publishing "bad news" or extreme viewpoints (good old Ken Rockwell was very much like this, only his views were more just personal preferences and often presented as such. Ergo he was extreme, but rather tame and not confrontational/hostile. Heck when he became popular many other reviewers poked the joke back such as commenting on how they used a tripod even if Ken God Rockwell didn't



Thanks.   Maybe it was just to make noise to get views, but  I did get the very strong impression this DOF guy just cannot see past his own faulty conclusion.  His video seems an excellent case of "When everyone else is wrong, it may be time to reconsider your own opinion".  

To me, Ken Rockwell seems a pretty good source of information. He doesn't have the smart aleck approach, he's just telling how it is.  He does have an impressive background and knowledge, always knows what he's talking about. And it's not just talk.  Lighting for example, it's clear he has been there, done that, and a lot of that.  If it is just a show, then he fools me. But there has been an non-mainstream opinion now and then.   He always explains those opinions clearly, and I'd say accurately and reasonably.  For example tripods...



> *Just Say No   *(Rockwell)
> 
> Don't use a tripod if you can help it. Having to carry one is a pain and thus cripples creativity. See Digital Killed My Tripod.
> 
> ...



Perhaps no one reads more than the first line, but I don't find any fault with it. It is exactly what I do, and did long before I ever read Rockwell.

He says use them when needed, but don't carry them around 24/7.  And mighty few of us do more.
I think it could compare to "don't use flash from the far row of grandstand or auditorium".


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## n614cd (Nov 19, 2018)

@WayneF 

Ok, your first post in this thread lost me. I am way to dense or you packed in to much info into a a short post. (I hope the latter more then the former).
I got lost when you jumped between the CoC and enlargement of the crop sensor. Any chance for a breakdown for dummies? 

Tim


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## Ysarex (Nov 19, 2018)

n614cd said:


> @WayneF
> 
> Ok, your first post in this thread lost me. I am way to dense or you packed in to much info into a a short post. (I hope the latter more then the former).
> I got lost when you jumped between the CoC and enlargement of the crop sensor. Any chance for a breakdown for dummies?
> ...



Since you asked I'll let Wayne get back to you, but, since I have this handy,  here's the graphic that goes with the answer.

Joe


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## WayneF (Nov 19, 2018)

n614cd said:


> @WayneF
> 
> Ok, your first post in this thread lost me. I am way to dense or you packed in to much info into a a short post. (I hope the latter more then the former).
> I got lost when you jumped between the CoC and enlargement of the crop sensor. Any chance for a breakdown for dummies?
> ...



Hi Tim.   I think I understand the question, but not fully sure what precise point the question is about.  I do wish I knew which sentence needs clarification, but will try again as follows:

OK, just to have a number, here speaking of a full frame 35 mm film frame, with classic CoC of 0.03 mm diameter.  That hypothetical 0.03mm standard is from the lens, and presumed present on the sensor image (not yet enlarged).  We compute Depth of Field distance limits using that CoC diameter, and  the lens parameters (focal length and aperture and focus distance), and the required sensor size enlargement to 8x10 inches (8x10 inches was just an arbitrary choice  for DOF calculations many decades ago, it had to have a number too).

That 0.03mm CoC was historically tested and declared to be the maximum limit (when on the full frame sensor) of what how much out-of-focus blur diameter can still be enlarged (by our sensor size enlargement) to still be acceptable when enlarged (larger diameter should be generally perceptible to our eye, but we say our eye cannot perceive less than 0.03 mm size when it is enlarged that much).

Because when we enlarge the sensor image to print an 8x10 inch print, that enlargement also increases the blur size, and the 0.03 mm diameter limit, to something larger (this full frame enlargement is near 9x larger), which then the previous 0.03 mm becomes about the size that our normal eye vision can probably detect as blur being present.  Seeing that blur becomes objectionable, which is why we defined that 0.03 mm maximum size.  If we instead had a smaller sensor, then there would  have been an appropriate smaller CoC. The blur can grow larger of course, further out of focus, but it becomes unacceptable if it does.

Depth of Field computes the distance limits where this viewing enlargement increases the 0.03 mm CoC limit diameter to be large enough for our eye to perceive its presence.

If the distance is within the DOF limit distances, it means the blur there is less than 0.03mm on the sensor. If outside the limits, the blur is worse.  Of course,  at any reasonable distance, there would really be no practical difference between one inch inside and one inch outside, it changes gradually across the boundary, but the math computes the precise hard boundary line.

I hope that was the question.


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## Ysarex (Nov 19, 2018)

@Tim, this might help:




 

Next a smaller aperture:



 

Next closer focus:



 

Joe


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## Tim Tucker 2 (Nov 19, 2018)

n614cd said:


> @WayneF
> 
> Ok, your first post in this thread lost me. I am way to dense or you packed in to much info into a a short post. (I hope the latter more then the former).
> I got lost when you jumped between the CoC and enlargement of the crop sensor. Any chance for a breakdown for dummies?
> ...



I'm not disagreeing with Wayne here, just using different words.

We asked the question as photographers about the limits of perceived sharpness ages ago. So they got a 10"x 8" print and asked, "how big does a dot have to be before it begins to look like a blur." What they were asking is how out of focus, or how blurred does a single point of focus have to be before we notice it as being out of focus on a 10"x 8" print.

When we had the answer it was a simple maths question to work out how big that dot had to be on the sensor to produce that dot on the finished print, basically divided it by the magnification factor. This is the circle of confusion size or CoC on the sensor. The constant is the size of this dot on a 10"x 8" print, it varies by sensor size because of the enlargement needed on smaller sensors to make a 10"x 8" print.


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## WayneF (Nov 19, 2018)

I like this picture of CoC from Wikipedia.   Focus is S1.  Blur C at distance S2 on left is CoC on sensor at c on right.


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## Christie Photo (Nov 19, 2018)

I confess I haven't CLOSELY read through all of the above, but I don't recall a single mention of a "normal lens."

I wonder if that's what causing all the confusion.

Those of us who used a variety of film cameras (old guys), know the normal focal length of a lens changes with the format of the camera.  AND since the vast majority of the camera market was not (and still isn't) the pros, most discussion about lenses refereed to 35mm cameras.  Oddly, it still does...  at least a bit.  Thus the terms "full frame" and "crop sensor."  These terms are relative to 35mm photography.  One sensor is simply a different "format" than the other.

A normal lens is one that approximates what we usually see with our eyes.  The focal length of a normal lens differs from format to format.  I seldom hear the term used anymore.

A normal lens for a 35mm camera is something like 47mm (most cameras were equipped with a 50mm or 55mm.  A normal lens for a square format 12o camera (6x6) is about 80mm.  And a normal lens for a 4x5 camera is about 6" (150mm).

So could this be contributing to the debate?  Hmmm.

-Pete


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## WayneF (Nov 19, 2018)

Christie Photo said:


> So could this be contributing to the debate?  Hmmm.



Yes, it is nothing new, it was indeed the same thing with film cameras.  We called the difference Film Format then, instead of Crop Factor.

Different sensor sizes or film sizes do have different "normal" lenses (with their focal length more or less considered approximately equal to the sensor or film diagonal dimension),  but not sure that "normal" otherwise really relates here, other than DOF does depend on focal length (as one factor), .

The "normal" focal length means they all give about the same normal photo view, about like we remember our eye saw, as you said.  But yes, to do that, the tiny sensors do have very short lenses, and larger sensors have longer lenses.

Zoom lenses are about universal now, and do strongly affect the field of view, so "normal" has lost much meaning today. The "regular" zooms should have one setting that could be called Normal, but we may not be aware of it today.

And another difference in this era is that the usual Equivalent Lens discussion is about DSLR with two bodies of two sensor sizes (full frame and cropped) which can both accept the same interchangeable lens. The different sensor size then causes the questions when using the same lens on both sensors.  The  Equivalent questions can get funny until they realize that a 50 mm lens is always 50 mm on any sensor, only the field of view changes with the sensor size.  But the Equivalent lens is mounted on the other full frame camera, if we are used to thinking in those terms.

Normal lens is more a moot point for compacts and phones, because they don't have interchangeable lenses.  There is no choice about lenses, other than the one built into the camera, so the camera simply does what it does.  Compacts have zooms, and phones seem a bit wide.  Many film cameras also did not have interchangeable lenses. Those that did then generally could not accept lenses for other frame sizes, so the question didn't arise that often (OK, view cameras could be an exception).


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## bhop (Nov 19, 2018)

Technically speaking, maybe not, but visually yes. IMO photography is based on visuals, not charts and numbers.


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## Ysarex (Nov 19, 2018)

Tim, Petrochemist, Braineack, Wayne, Derrel, et al. It looks like we're all wrong after all. 

Here's a new one making the rounds and the evidence against us is just too overwhelming:






Joe


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## bhop (Nov 19, 2018)

Ysarex said:


> Tim, Petrochemist, Braineack, Wayne, Derrel, et al. It looks like we're all wrong after all.
> 
> Here's a new making the rounds and the evidence against us is just too overwhelming:
> 
> ...




Darn it!


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## donny1963 (Nov 19, 2018)

Braineack said:


> donny1963 said:
> 
> 
> > every lens made on earth craps out the same light same bokah same everything regardless of what sensor it is used on.
> ...


what are you trying to imply that i would not be able to follow? 
really?

also this does not disprove that DOF does not change when you take the same shot with the same lens and same distance  using both a crop sensor camera and then full frame or even medium format, ..
DOF does not change, the crop changes, but not the DOF the DOF is exactly the same a 50 mm lens craps out the same amount of DOF on both a crop sensor camera and  a full frame camera, the only thing that changes is the crop of course, but the lens still works the same way as far as DOF goes.. Period & FACT!!!!!!!


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## Ysarex (Nov 19, 2018)

donny1963 said:


> Braineack said:
> 
> 
> > donny1963 said:
> ...



This does prove you're wrong.  Go ahead and post a link to any DOF calculator that proves you're right. You can't because you're proven wrong.




Joe


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## donny1963 (Nov 19, 2018)

Ysarex said:


> Tim, Petrochemist, Braineack, Wayne, Derrel, et al. It looks like we're all wrong after all.
> 
> Here's a new one making the rounds and the evidence against us is just too overwhelming:
> 
> ...


there you go that proves what i said,  if your standing in the exact same place, feet glued to the floor using the same lens it won't matter if your shooting with a crop sensor full frame or even medium format Sensor size has nothing to do with DOF NOTHING!!!!
it doesn't not change it a bit, your just recording the same exact thing on a larger recording sensor that is it..
people get confused saying the DOF changes using full frame vs crop sensor because they are re-positioning them self to get the same composition of the shot.
so naturally the DOF will change if you change your distance because on smaller crop sensors vs larger sensors, they have to move further back to get the same fame shot so they are getting a different DOF But it has nothing to do with the sensor at all where the DOF changes only because they are a different distance.....


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## donny1963 (Nov 19, 2018)

Ysarex said:


> donny1963 said:
> 
> 
> > Braineack said:
> ...


your video you just posted proves what i sand and disproves what you said lol


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## donny1963 (Nov 19, 2018)

bhop said:


> Technically speaking, maybe not, but visually yes. IMO photography is based on visuals, not charts and numbers.


Technically and visually, what i said was 100% correct how could the sensor size have anything to do with changing DOF Except for some one who would step a few feet back to get the same shot as they got with the full frame, while uing crop sensor.  that is the only reason DOF changes has nothing to do with the sensor size..
Sensor size will not change anything..


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## Ysarex (Nov 19, 2018)

donny1963 said:


> Ysarex said:
> 
> 
> > Tim, Petrochemist, Braineack, Wayne, Derrel, et al. It looks like we're all wrong after all.
> ...



So you didn't actually look at the DOF examples I posted?! Here I'll post it again:



 
Notice the subject distance for both cameras. It's 10 feet for both -- no distance change. Same f/stop for both and same lens focal length for both. The only change is the sensor size from FF to crop and the DOF changes.

You are proven wrong by your own criteria.

Joe


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## Ysarex (Nov 19, 2018)

donny1963 said:


> your video you just posted proves what i sand and disproves what you said lol



I posted that video as another example of a blathering idiot making the same wrong claims and then some.

Here you go again. Proof that you're wrong. How about instead of just ranting nonsense you post a DOF calculator that supports your claim?




 
Joe


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## Ysarex (Nov 19, 2018)

donny1963 said:


> bhop said:
> 
> 
> > Technically speaking, maybe not, but visually yes. IMO photography is based on visuals, not charts and numbers.
> ...



Then explain why this DOF calculator proves you're wrong:



 

Joe


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## greybeard (Nov 19, 2018)

Every so often one of these things come up and we go on for days with it.  It's fun I know but, this is all about how we try to explain things and has nothing to do with anything that matters.  If you have any experience with multiple formats you understand how focal lengths differ with perspectives and DoF when used between formats.


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## n614cd (Nov 19, 2018)

@Ysarex @Braineack @Derrel @WayneF @Tim Tucker 2 

I think that is everyone! 
It all sort of makes sense. Not sure I can regurgitate it yet.
The only two things I do not get, one why is it called "Circle of Confusion"? 
And secondly, it is stated as fact in multiple places the formula, and specific values for CoC. I am perfectly willing to accept 0.3mm for full frame and 0.2mm for a standard 1.5 crop sensor.  Even reading the Wiki page for some reason I cannot wrap my head around this explanation. It intuitively makes sense to me, but I just do not follow the "official" definition.

Tim


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## n614cd (Nov 19, 2018)

greybeard said:


> Every so often one of these things come up and we go on for days with it.  It's fun I know but, this is all about how we try to explain things and has nothing to do with anything that matters.  If you have any experience with multiple formats you understand how focal lengths differ with perspectives and DoF when used between formats.



Well, I am not a grey beard yet, just going bald 
Anyway, as a hobby photographer I have the usual 35mm before I "got the bug". When I did get the bug it was in digital, and I started with a crop sensor, and then went full frame very early. So I do not have the multiple formats background.  So for me, I enjoy learning on these threads. It helps me actually understand what I have found out via experience.

Tim


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## n614cd (Nov 19, 2018)

donny1963 said:


> bhop said:
> 
> 
> > Technically speaking, maybe not, but visually yes. IMO photography is based on visuals, not charts and numbers.
> ...



Donny,

What is DoF? Start with the fundamentals please.

Tim


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## donny1963 (Nov 19, 2018)

Ysarex said:


> donny1963 said:
> 
> 
> > bhop said:
> ...


it's wrong because Sensor size would have nothing to do with changing the DOF NOTHING!!


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## n614cd (Nov 19, 2018)

donny1963 said:


> it's wrong because Sensor size would have nothing to do with changing the DOF NOTHING!!



Repeating the same thing, with exclamation points does not prove or make your case. Start with the basics, and answer my question in post #51

Tim


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## Ysarex (Nov 19, 2018)

n614cd said:


> @Ysarex @Braineack @Derrel @WayneF @Tim Tucker 2
> 
> I think that is everyone!
> It all sort of makes sense. Not sure I can regurgitate it yet.
> ...



Don't worry about the name. The name I think derives from the most common description of what we're measuring. A lens is used to focus a sharp dot -- how about a pin head. What we want to know is at what point do you see the pin head as blurred versus still sharp.

It's really just an empirical measurement to account for the acuity of human sight. If we were creating DOF tables for eagles we'd need different CoC values. So all you really need to know is that it's an empirically derived control value that factors human visual acuity and a magnification factor for film/sensor size into the DOF equations.

Joe


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## n614cd (Nov 19, 2018)

Ysarex said:


> Don't worry about the name. The name I think derives from the most common description of what we're measuring. A lens is used to focus a sharp dot -- how about a pin head. What we want to know is at what point do you see the pin head as blurred versus still sharp.
> 
> It's really just an empirical measurement to account for the acuity of human sight. If we were creating DOF tables for eagles we'd need different CoC values. So all you really need to know is that it's an empirically derived control value that factors human visual acuity and a magnification factor for film/sensor size into the DOF equations.
> 
> Joe



lol, the number of times I have had a teacher tell me that in college. 
I always ask why.... drove my parents crazy (still does), and also my teachers.

Tim


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## Ysarex (Nov 19, 2018)

n614cd said:


> Ysarex said:
> 
> 
> > Don't worry about the name. The name I think derives from the most common description of what we're measuring. A lens is used to focus a sharp dot -- how about a pin head. What we want to know is at what point do you see the pin head as blurred versus still sharp.
> ...



OK -- damn! I'm a college teacher. So here's a couple sentence from my class notes that I give my students:

Used in photography the size of the circle of confusion is a complex value dependent upon the viewing distance, degree of enlargement and therefore size of the camera sensor, and the size of the photographic print/display and must be adjusted to match all these variables. For an 8x10 photograph from a 35mm film negative a commonly agreed upon size for the circle of confusion is .03175mm. What we've done in the industry is make some assumptions about normal print size and then establish common circle of confusion values tied to the size of the camera sensor/film. For more detailed info: DOFMaster.

Here's another way to think about it: If we place a point before a lens in the plane of focus, the point will appear as a point on the film/sensor. As we move the point away from the plane of focus it's image on the film/sensor will blur into a disk. At the threshold beyond which we can see the difference between the focused point and the out of focus disk we find the diameter of the circle of confusion.

Joe


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## n614cd (Nov 19, 2018)

My parents are retired college professors; so I get the struggle.

Anyway, between your notes and other pages. Is it safe to assume CoC was measured via empirical testing. The result of which formulas were defined to predict other values?
The part I was struggling with was going from nothing to formula to value...

Tim

Sent from my SM-J737T using Tapatalk


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## Ysarex (Nov 19, 2018)

donny1963 said:


> Ysarex said:
> 
> 
> > donny1963 said:
> ...



So we've already proven that you're wrong. I've shown you the proof probably close to a dozen times now. My proof that your wrong is mathematically derived at DOF Master -- a recognized authority.



 
Further back in this thread are posts from Petrochemist and Wayne that explain why you're wrong. To calculate DOF we use a variable we call CoC and the value of that variable is in part predicated on sensor size. The common table of sensor size/CoC values was posted here in post #30 -- go look at it. If you change the value of a variable in an equation the equation produces a different result. Change sensor size and you change the value of CoC and the DOF changes.

Now that proves you're wrong. You've offered NOTHING to prove otherwise.

Standing in front of a mathematical proof that shows why you're wrong and just repeating your mistake is a pretty dumb thing to do.

Prove what you say -- here you'll find all the math that proves you're wrong: Depth of field - Wikipedia *show us where that math is incorrect.*

Joe


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## Ysarex (Nov 19, 2018)

n614cd said:


> My parents are retired college professors; so I get the struggle.
> 
> Anyway, between your notes and other pages. Is it safe to assume CoC was measured via empirical testing.



BINGO. If you look at tech explanations you're going to see formulae used for CoC calculation but that's the real bottom line. It is an empirically derived value that reflects human eyesight acuity -- we add into it values to account for enlargement size print viewing distance.

Any good DOF calculator will allow you to enter your own CoC values which you can select to tailor results to your usage and liking.

Joe



n614cd said:


> The result of which formulas were defined to predict other values?
> The part I was struggling with was going from nothing to formula to value...
> 
> Tim
> ...


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## AlanKlein (Nov 19, 2018)

Ysarex said:


> donny1963 said:
> 
> 
> > Ysarex said:
> ...



Depth of field remains the same with the same lens and with different crop sensors.  What's happening is the crop sensor is just capturing a portion (let's say 1.5x or 2x) of what a full frame sensor would capture.  So when you blow it up to match the FF, the depth of field is reduced.  It's like changing a normal lens to a telephoto lens shooting from the same distance.  The DOF is reduced.  See my earlier post. Depth of field (DOF) does NOT change with sensor size


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## WayneF (Nov 19, 2018)

n614cd said:


> I think that is everyone!
> It all sort of makes sense. Not sure I can regurgitate it yet.
> The only two things I do not get, one why is it called "Circle of Confusion"?
> And secondly, it is stated as fact in multiple places the formula, and specific values for CoC. I am perfectly willing to accept 0.3mm for full frame and 0.2mm for a standard 1.5 crop sensor.  Even reading the Wiki page for some reason I cannot wrap my head around this explanation. It intuitively makes sense to me, but I just do not follow the "official" definition.
> ...



Tim, I think you refer to the page at Circle of confusion - Wikipedia

Circle of Confusion is the larger unfocused blob of an unfocused spot in a photo.  You have surely seen unfocused areas before. That articles first image in top right page corner shows a diagram of it.  An unfocused blob just spreads and grows larger.




About 3/4 way down that page are quotes of articles from 1829 and 1832, calling it Circle of Confusion.  I don't know if that was first usage, but it already had that name then.  That was a different time, not much was yet known about optics, and the unfocused blob was indeed a Circle of Confusion (there was no detail in it).  That date was before cameras, that was about microscope and telescope lenses. Then the 1866 article after Daguerre had his early camera in 1840.  At at the 1889 article, we had the first Kodak Brownie (one year before).  Anyway, it is an early name for a very old concept.  And sort of a quaint name from different times.  But they were interested in calculating CoC size then.

The first text line (by that top diagram, about the diagram) is:


> Diagram showing circles of confusion for point source too close, in focus, and too far
> In optics, a *circle of confusion* is an optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source. It is also known as *disk of confusion*, *circle of indistinctness*, *blur circle*, or *blur spot*.



So CoC is simply the name of the larger blob diameter of a (tiny) unfocused point source, like the diagram shows. That should be clear enough.  It is a spot of blur.  If we are going to compute its size, we need a name for it. 

Depth of Field calculators use the term CoC slightly differently for their purpose, as the name for the specification for the maximum allowable unfocused blob that is still too small for our eyes to see when enlarged to a usable viewable print (the 0.03 mm for full frame computations is a hypothetical dimension used for reference).   And specifically, for standardization,  the spec for DOF is to use an 8x10 inch print to compute DOF on.  So it computes the unfocused blob diameters and the DOF distance limits are where the CoC blobs grow larger than this reference CoC, and thus becomes large enough to be visible blur to our eye when enlarged for viewing.  If Depth of Field is said to be say 10 to 20 feet,  and it was a full frame sensor (0.03 mm CoC) enlarged to 8x10 inch viewing size, then the CoC at exactly both 10 and 20 feet is 0.03 mm (regardless if there is any unfocused blob there or not). That 0.03 mm is on the sensor, it is larger on the enlarged print, at just the limit of our eyes capability there. And larger outside that range (blurred), and less inside it (not blurred).  But the calculated DOF limits means the CoC calculation that did reach that maximum allowable amount (at 10 or 20 feet) could still call it sharp enough for our eye, when enlarged to a 8x10 inch print size.

The arguments (like Donny here) that the sensor size has no effect on the DOF  simply don't know enough about DOF yet.  DOF has been studied for more than 100 years, but Donny hasn't actually started  yet. Sounds like he just found crap on the net that gave him the idea. The net is sort of a strange world, some of it is Not to be trusted.    Any idiot can post anything. Some of it may be good entertainment.

Yes, it is certainly true that the sensor has no effect on the image that the lens creates.  And that is what Donny is trying to say.  However, DOF is a very different deal, because the sensor, and even most film sizes are simply too small to view any critical detail. We do not look at them, we always make larger prints, or show it large on a video monitor, or project a slide or movie on a large screen, so that we can see it big.  Or use a 10x loupe if we do have to look at the negative.  And we want that enlarged print to look good too, so we compute DOF on that enlarged size of blur.

Of course, that enlargement certainly enlarges blur too, and all that matters is how that enlargement looks.  The Depth of Field formula computes the CoC blur enlarged to 8x10 inch print size.  And a tiny sensor certainly requires much more enlargement to get to 8x10 inch size, *so yes, sensor size ABSOLUTELY affects Depth of Field calculations*.  Sensor size does not affect the image already on the sensor, but it does of course affect the images that we enlarge from it.

Technically, the choice of specification for maximum allowable CoC is what adjusts DOF for enlargement size.  For the 35 mm film frame, Sensor diagonal / 1442 = 0.03 mm (common in Japanese cameras, or we still see /1500 = 0.0288 mm sometimes).  The Sensor diagonal size is what adjusts CoC in the DOF formula for the enlargement to 8x10 inch print size.  A smaller sensor computes a smaller CoC, which is worse DOF due to the greater enlargement required.  HOWEVER, the smaller sensor necessarily must use a much shorter lens on its cropped size, which works oppositely in the DOF formula.   Not equally,  a greater effect, but oppositely.


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## Ysarex (Nov 19, 2018)

AlanKlein said:


> Depth of field remains the same with the same lens and with different crop sensors.



Not sure what you're trying to say with that sentence. Crop sensor typically refers to an APS sensor and different APS sensors are still APS sensors so they're the same size. So yep, DOF stays the same with the same lens on any APS size sensor.



AlanKlein said:


> What's happening is the crop sensor is just capturing a portion (let's say 1.5x or 2x) of what a full frame sensor would capture.  So when you blow it up to match the FF,



You can't blow it up to match the FF. The FF image contains more information -- that info is not in the crop sensor image. If you use both cameras to take the same image the crop sensor image will have more DOF than the FF image. If you use the same lens from the same place on both cameras the FF image will have more DOF and will be a different image showing a wider FOV.

Joe



AlanKlein said:


> the depth of field is reduced.  It's like changing a normal lens to a telephoto lens shooting from the same distance.  The DOF is reduced.  See my earlier post. Depth of field (DOF) does NOT change with sensor size


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## petrochemist (Nov 20, 2018)

donny1963 said:


> what are you trying to imply that i would not be able to follow?
> really?
> 
> also this does not disprove that DOF does not change when you take the same shot with the same lens and same distance  using both a crop sensor camera and then full frame or even medium format, ..
> DOF does not change, the crop changes, but not the DOF the DOF is exactly the same a 50 mm lens craps out the same amount of DOF on both a crop sensor camera and  a full frame camera, the only thing that changes is the crop of course, but the lens still works the same way as far as DOF goes.. Period & FACT!!!!!!!



Perhaps we need to go back to basics & define DOF?
Depth of field is the region of the subject that will look acceptably sharp in the image.
If we magnify the image a given degree of blur will be more noticeable, so how can the region that is acceptably sharp be the same???

Take any image & view it full screen unmagnified & access the limits of what looks focused to you. Magnify the same image 2 fold & view in the same way (effectively cropping the image) you WILL see more blur than originally the DOF is changed.


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## Tim Tucker 2 (Nov 20, 2018)

bhop said:


> IMO photography is based on visuals, not charts and numbers.



Absolutely, and highlights the many problems with misconceptions and theories in threads such as these.

What we try to do as humans is *rationalise a logic* to explain how things work, but what generally happens that we create a framework or narrative of logic to satisfy our desire to have it understood. We then defend that narrative and refuse to *see* it in any other way, it becomes a loggerheads to and fro revolving around a simple "I'm right and you're wrong," *discussion*.

@donny1963, like many others, is basing that logic around an understanding of how cameras work. And just like many others there are blindingly obvious contradictions in the logical narrative that we create, leaps and assumptions that have no basis in actual observation but only in how we think it *should* work.

A lot of it fails because of one simple and obvious flaw:

*We fail to look objectively and understand how we see through our own human eyes.*

Instead we see what we understand and have decided is true, we glance at things to re-inforce our own pre-determined opinions.

In trying to create a logical narrative @donny1963 is following the logic of how a lens forms an image on a sensor. It completely ignores that we see images through human eyes with all the distortions of perception that comes from viewing with human eyes. It completely ignores over half the equation of how images are formed. Images are formed on a 2D output, then light reflected/generated from the image is focussed by our eyes and the image is perceived and interpreted through human vision and human understanding.

Images are not and never have been about how a camera sees but always have been based on an understanding of how we as humans see an react to what we see. The fundamental error here is not that the exact same lens behaves in the exact same way regardless of the sensor, but that it tries to describe the whole process of forming an image by how the lens works alone. It pays absolutely no attention to either understanding the subject or how we as humans view and interpret the finished image.

Here is an image to try and demonstrate this, *it is exactly the same image and so formed by exactly the same lens on exactly the same sensor*:






You may be fooled into thinking that the image is crisp and sharp when you glance, but actually there is very little that is either sharp or in focus.

Here it is again enlarged:





You can see that your entire assumptions of sharpness and therefore what is actually in focus change simply by altering the size of the finished image against the same viewing distance. Perception of sharpness is illusion and dependant on the assumptions we make when viewing the finished image with human eyes.

DOF is all about how we *perceive sharpness* in a finished image, it's about human perception and has far less to do with aperture and how a lens works than many photographers are prepared to admit.

To go one stage further and demonstrate that understanding the subject is more relevant than how the lens forms the image here is another one:





You may perceive that the near water is sharp, but then it remains sharp beyond the remains of the pier that is clearly out of focus. I know that many will make assumptions based on their understanding of photography in that they may assume some focus stacking. But that is an example of trying to quantify what you see into the mechanics you understand. The truth is that there is no focus stacking and the effect is simply due to smooth reflections having a higher acutance and therefore appearing sharper to the human eye.

What I'm trying to illustrate here is that how we interpret sharpness in images is mainly down to human perception. That by trying to force a complete understanding based upon only how a lens works we completely fail to understand how the illusion of DOF and sharpness really works in a finished image. The whole premise upon which DOF is based, human perception and not lens mechanics.


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## BananaRepublic (Nov 20, 2018)

Is light a particle or a wave ?


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## Ysarex (Nov 20, 2018)

petrochemist said:


> donny1963 said:
> 
> 
> > what are you trying to imply that i would not be able to follow?
> ...



*Exactly!* You had this right back at the beginning of the thread in post #5 -- now we're at post #65. *DOF is defined on the print/final image at the final enlargement size and viewing distance.* That's where blathering idiot in the video trips himself up. He's trying to define DOF as something that's happening at the film/sensor plane. DOF doesn't happen there -- it's not defined there. You can talk about what's happening with the projected image from the lens on the film/sensor but you can't call that DOF. That's not how DOF is defined.

Most DOF calculators and basic equations assume default values for print/image size and viewing distance but just because those are assumed doesn't mean they go away. The DOF calculator at Cambridge in Colour is instructive. It allows you to change print size and viewing distance. *The definition of DOF requires those variables. *Blathering idiot left them out of his video.





There is a reason why DOF is defined the way it is and there is a reason the variables used in the equations to calculate DOF are subject distance, focal length, f/stop, sensor size, print size and print viewing distance. We could do what this blathering YouTuber: 



does and take f/stop out of the equation and use aperture (entrance pupil) instead. But which one of us while taking a photo knows the diameter of their lens aperture. Tim has hinted at or plain said this back through this thread: *That's not helpful to photographers.* Photographers are very familiar with lens focal length, f/stop and subject distance (the three variables they are likely to be able to change while taking a photo). DOF is complicated enough and it doesn't simplify the topic to force photographers to use uncommon variables like entrance pupil.

We can express DOF in different and possibly simpler terms but not in* more helpful*/useful terms.

DOF = magnification + f/stop. Yep I always know the magnification when I'm taking a photo -- *not very helpful.*

Put a tripod on the ground and don't move it. Mount any camera you like with any size film/sensor. In every photo without changing the subject position or tripod position set the exact same FOV and at the same physical aperture -- all cameras will render the same DOF as viewed in an 8x10 print. I didn't have to mention focal length, and I almost sound like the YouTuber I just posted a link to above, but I controlled for focal length by specifying a constant FOV (he missed that). This kind of stuff can be instructive. It's good to know that focal length and subject distance = magnification. But when we're out there taking photos this kind of stuff is *not very helpful. *Tim is spot on from back in post #2 with his comment about "equivalence priests," "_I find that it does allow you a more complete understanding of the relationships between the fundamental controls of the camera, but is also used as a sort of *geek speak* by those who want to create the illusion that they understand photography and digital better than anybody else, rather than my preferred method of using understanding to create better images._"

More than 100 years before any of us were born DOF was well understood by our industry. And those shoulders we stand on very wisely defined and described DOF in the *most helpful terms* they could so that we as working photographers can think about f/stop and not entrance pupil. So that we don't have to figure magnification but rather pay attention to our lens focal length and subject distance. And finally we can view the expected result in our finished photo.

Way back in post #27 Braineack put up what is arguably the *most helpful* post in the entire thread. He posted the two photos in which you can see the obvious -- hey look at that: changing sensor size changed the DOF. Look at any standard definition of DOF and you're likely to see the term "acceptably sharp." Think about that term -- "acceptably?" We use math equations to calculate DOF. Imagine a mathematician saying 2 + 2 = something acceptably close to 4. DOF as defined is a phenomenon of human visual perception. It defines an aspect of how we see photographs. It is not defined as what a lens craps out.

To control DOF I can't think of a *more helpfu*l way to explain it to photographers other than it's a function of subject distance, focal length and f/stop with sensor size and print enlargement/viewing distance functioning as fixed variables not normally accessible to change in the field.

Joe
*
*


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## deeky (Nov 20, 2018)

Ysarex said:


> DOF as defined is a phenomenon of human visual perception. It defines an aspect of how we see photographs. It is not defined as what a lens craps out.



This, right here.  I've been watching this post, but I have to admit I just didn't have the brain energy left to read all of them in depth.  This right here, though, I think is the issue of contention in all of this.  This made it click for me more than the other charts and graphs and equations.  And perhaps more importantly, it takes photography back to the art that it always has been rather than mere science.

Thank you for the clarification.


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## markjwyatt (Nov 20, 2018)

Christie Photo said:


> I confess I haven't CLOSELY read through all of the above, but I don't recall a single mention of a "normal lens."
> 
> I wonder if that's what causing all the confusion.
> 
> ...



Peter- I agree with you. This is what is missing, and [I believe] is key to understanding this issue [see my note at the bottom].

If you compare normal lens on a 4/3 sensor with a given shot (say subject at 6', f5.6, 1/125 s) to a full frame with its normal lens (subject at 6', f5.6, 1/125 s)- I.E., The same picture, the 4/3 camera will have more depth of field. This is the case. Some say it does not matter. You can put on a longer lens and stand back. But you cannot always stand back that far. You may run into a wall, other objects may start interfering with the shot etc. Now this does not make the problem insurmountable. Maybe you want the greater depth of field. Maybe you can shoot the 4/3 at f2.8 and 1/500s. In general you just use whatever tool you have.

It is difficult or even impossible to get the same view, perspective, and DOF at the same distance with a full frame and a crop camera. If your shooting style is to be in close and get small DOF, with normal perspective relations then a larger sensor will help. If you want large DOF then crop may be an advantage. I bring this up at camera shops where they push 4/3, and they always say it is proven a myth. But they seem to ignore this point. In terms of effect on a given image, I do not think in terms of sensor size and 35mm equivalents, but rather am I shooting a normal, wide or long lens, and in those cases, whether it is full frame or crop, or even tiny sensors or iPhone it makes a difference in DOF.

Using the Cambridge DOF calculator (default parameters- 25 cm or ~10" viewing distance, 10 in. print, mfr standard vision);
Compare full frame and 4/3, same picture, same distance, same exposure and same aperture:
A Flexible Depth of Field Calculator

Focus 5m
aperture f/5.6
(4/3 crop factor = 2, assume same shutter speed both cameras, thus same exposure and aperture)

Full frame 50mm lens: 3.69 < DOF < 7.75 meters, FOV 14' 2.00"
4/3 crop 25 mm lens: 2.92 < DOF < 14.52 meters, FOV 14' 2.00"

(FOV: Depth of Field (DoF), Angle of View, and Equivalent Lens Calculator | Points in Focus Photography): note this calculator uses different parameters for DOF and the DOF numbers are a little different, but close and consistent.

Now the 4/3 also has a 2x factor on the aperture, so if we went to f/4 (and doubled the shutter speed)
4/3 crop 25mm lens: 3.31m< DOF < 10m a bit closer to the full frame, but still greater DOF, plus we seem to need faster lenses (and potentially shutters too) on the 4/3 to get close to equivalency.

NOTE: I posted this response to Peter, then read Joe's post above and questioned my conclusions. I then added the numbers and feel my conclusions are sound, but not consistent with Joe's. My conclusion would say that a "normal" lens on a 4/3 camera (taken as 25mm) with equivalent distance, focus, and aperture (and exposure overall if ISO were the same, but this is actually somewhat  irrelevant) would have greater DOF than a "normal" lens on a full frame (taken as 50mm). The normal lenses have the same FOV, and I would suspect the same perspective (i.e, normal).  Similar conclusions would apply for equivalent wide and long lenses. This is getting interesting and I am learning a lot. My conclusion was intuitive based on experience but not math or experiments, and Joe suggested it was wrong (and I certainly could be wrong).


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## markjwyatt (Nov 20, 2018)

Ysarex said:


> ...
> Put a tripod on the ground and don't move it. Mount any camera you like with any size film/sensor. In every photo without changing the subject position or tripod position set the exact same FOV and at the same physical aperture -- all cameras will render the same DOF as viewed in an 8x10 print...



Joe- Did I miss something? See above post (Depth of field (DOF) does NOT change with sensor size)

The only thing missing from the quote and my example is perhaps the same focus point, but I think that is implied and very important. Another issue you mentioned is magnification, but I suspect these are equivalent in this case?


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## markjwyatt (Nov 21, 2018)

Tim Tucker 2 said:


> ...
> 
> Here it is again enlarged:
> 
> ...



I was always taught with portraits that the key is to have the catch light in the eyes sharp. Get that and the impression of sharpness is favorable. Lose that and you lose the image. In your image, the catch light is pretty sharp.

Here is a picture I took of my dog. I really did not get the catch lights perfectly sharp, and there is an impression of softness (I still like the image but would prefer the eyes to be sharper). If you look closely, the collar is pretty sharp.




Taffy Pose by Mark Wyatt, on Flickr


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## Ysarex (Nov 21, 2018)

markjwyatt said:


> Christie Photo said:
> 
> 
> > I confess I haven't CLOSELY read through all of the above, but I don't recall a single mention of a "normal lens."
> ...



Your conclusions are sound and consistent with mine.



markjwyatt said:


> My conclusion would say that a "normal" lens on a 4/3 camera (taken as 25mm) with equivalent distance, focus, and aperture (and exposure overall if ISO were the same, but this is actually irrelevant) would have greater DOF than a "normal" lens on a full frame (taken as 50mm).



I concur but we need to be clear what you mean when you say aperture. If you take the same photograph 4/3 and FF (same perspective, same FOV, same subject focus point) at the same f/stop for both lenses the 4/3 photo will have more (deeper) DOF. I've never said otherwise.

Joe



markjwyatt said:


> The normal lenses have the same FOV, and I would suspect the same perspective (i.e, normal).  Similar conclusions would apply for equivalent wide and long lenses. This is getting interesting and I am learning a lot. My conclusion was intuitive based on experience but not math or experiments, and Joe suggested it was wrong (and I certainly could be wrong).


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## markjwyatt (Nov 21, 2018)

Ysarex said:


> at the same* physical* aperture



Ok, so by physical aperture you mean the same actual DIAMETER of the aperture, not the same f/stop number/ratio. What matters to photographers when shooting tends to be f/stop, not physical aperture, but I get what you are saying.

So, this still holds (and I think this is what matters most to photographers shooting pictures and puts the argument in the clearest context as suggested by Peter earlier):

My conclusion would say that a "normal" lens on a 4/3 camera (taken as 25mm) with equivalent distance, focus, and aperture (and exposure overall if ISO were the same, but this is actually irrelevant) would have greater DOF than a "normal" lens on a full frame (taken as 50mm).

The normal lenses have the same FOV, and I would suspect the same perspective (i.e, normal). Similar conclusions would apply for equivalent wide and long lenses.


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## Ysarex (Nov 21, 2018)

markjwyatt said:


> Ysarex said:
> 
> 
> > ...
> ...



Yes, I think so. I used that as an illustration of the kind of presentations that are not helpful. I said same physical aperture not aperture and not f/stop. In that example each lens used must have the same entrance pupil. So if a 4/3 camera is one of the cameras used and has an entrance pupil of 10mm then if a medium format camera is used as well the lens would also have to have an entrance pupil of 10mm. The difference in f/stops there would be quite substantial.

Joe



markjwyatt said:


> See above post (Depth of field (DOF) does NOT change with sensor size)
> 
> The only thing missing from the quote and my example is perhaps the same focus point, but I think that is implied and very important. Another issue you mentioned is magnification, but I suspect these are equivalent in this case?


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## Ysarex (Nov 21, 2018)

markjwyatt said:


> Ysarex said:
> 
> 
> > at the same* physical* aperture
> ...



Yes. You're getting it.



markjwyatt said:


> What matters to photographers when shooting tends to be f/stop, not physical aperture,



Yes! That was my point. The YouTube blathering idiots are not helping anyone with their usually misguide and misunderstood contortions.



markjwyatt said:


> but I get what you are saying.
> 
> So, this still holds (and I think this is what matters most to photographers shooting pictures and puts the argument in the clearest context as suggested by Peter earlier):
> 
> My conclusion would say that a "normal" lens on a 4/3 camera (taken as 25mm) with equivalent distance, focus, and aperture (and exposure overall if ISO were the same, but this is actually irrelevant) would have greater DOF than a "normal" lens on a full frame (taken as 50mm).



Absolutely! That's a fact. And that means sensor size is a determinant factor for DOF.



markjwyatt said:


> The normal lenses have the same FOV, and I would suspect the same perspective (i.e, normal). Similar conclusions would apply for equivalent wide and long lenses.



Do not make the error of assigning perspective to lens focal length. Perspective is a function of where you put the camera, period. Lens focal length does not determine perspective. So perspective means both photos taken from the same place. This is a critical factor. In order to compare same photos they must both be taken from the same place -- same perspective.

Joe


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## markjwyatt (Nov 21, 2018)

Joe- I think we are entirely consistent. Sorry for not considering your "how not to do it" aspect! We actually use that approach in selling software, we say How Not to Do "X", then list three easy ways that people use to try and handle "X" which we then demonstrate not to be correct. We then follow by demonstrating how our software [or more generally the theoretically preferable approach] is the best way to handle "X".


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## markjwyatt (Nov 21, 2018)

Ysarex said:


> ...
> Do not make the error of assigning perspective to lens focal length. Perspective is a function of where you put the camera, period. Lens focal length does not determine perspective. So perspective means both photos taken from the same place. This is a critical factor. In order to compare same photos they must both be taken from the same place -- same perspective.
> 
> Joe




Maybe "perspective" is not the correct term(s). By perspective I am talking about the effect I get when I stick a 300mm lens on a 35mm camera, or a 12mm lens for a different perspective (i.e., scrunching or widening of distance, as well as distortions, etc.). A "normal" lens is intended to give a normal (to the typical human eye) relation between far and near distances. Telephotos and wide angles tend to change those relations.


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## markjwyatt (Nov 21, 2018)

Ysarex said:


> ...that means sensor size is a determinant factor for DOF...Joe



Generally when I talk to people in camera stores I basically say that and they always try and shoot me down. When I bought my Fuji XT-2, I tested it in place, and the guy kind of looked at me funny as though thinking, 'ok, if it makes you fell better,  but it does not matter'. It does matter, but does not necessarily make one format better or worse than another, just different, and you need to understand those differences.


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## Ysarex (Nov 21, 2018)

markjwyatt said:


> Joe- I think we are entirely consistent.



Yes. Sensor size is absolutely a DOF determinant factor. Both of the YouTube vidiots featured in this thread presented their nonsense recently. I've had to address both of them in different forums for the last two weeks and clear up the rubbish they've been dumping. Don Quixote here tilting at YouTube windmills -- good thing I'm retired.

Joe



markjwyatt said:


> Sorry for not considering your "how not to do it" aspect! We actually use that approach in selling software, we say How Not to Do "X", then list three easy ways that people use to try and handle "X" which we then demonstrate not to be correct. We then follow by demonstrating how our software [or more generally the theoretically preferable approach] is the best way to handle "X".


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## Ysarex (Nov 21, 2018)

markjwyatt said:


> Ysarex said:
> 
> 
> > ...
> ...



Be careful with that thinking. This is a case of cause and effect and correlation being very closely related. It can matter at some point that you have the cause/effect relationship straight. Perspective is the rendering of the relationship of objects in 3D space. It is only determined by camera position. We get a chicken/egg thing happen here with very long and short lenses. A long lens is only good for photographing distant objects and so we render those distant objects with what appears to be compressed perspective. Is that a function of the lens or a function of the camera subject distance? We normally use long lenses to photograph far away objects but is the compressed perspective due to the lens or due to the fact that we're far away? It's not the lens it's our physical distance from the subject -- our 3d relationship with the other objects in 3d space.

Joe


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## Ysarex (Nov 21, 2018)

markjwyatt said:


> Ysarex said:
> 
> 
> > ...that means sensor size is a determinant factor for DOF...Joe
> ...



Different is good! I have a little compact I use to take a lot of photos of my wife's garden and the flowers there. It has a dinky little 1/1.7 sensor in it. I can set the f/stop to f/3.2 and get great photos of close-up flowers that a FF camera would struggle to give me at f/9.5. Understand the differences and take advantage of them. What a mess we'd be in if we were all restricted to using only one type of camera!

P.S. Your people in the camera stores need some education.

Joe


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## Tim Tucker 2 (Nov 21, 2018)

Ysarex said:


> markjwyatt said:
> 
> 
> > Ysarex said:
> ...



To be a little more precise, *perspective is entirely from the position of the observer*.

It is a *chicken and egg* as what is actually happening is easy to mis-interpret if you only try to define it by how a lens works. Focal length has no effect on perspective, it is entirely dependant on the camera position. *But*...

Perspective is also dependant on the distance you view the print. Though because your eye presents you with a consistent view of the world, one where distances are constant and understood perspective doesn't really change as you change your position to a print. It's not a linear relationship and another demonstration that relationships in images are not defined entirely from the lens but also from our human perception when we view the images. It is why standard lenses are called *standard*, because they present a natural perspective, or the same perspective when we view the print. If you view a print from the same relative position as the camera we see the perspective from the camera position (standard lens for the format), if you view a print from a position that's not the same relative to the camera position you see a distortion of perspective.

Very basically FOV is not recorded in a print so when you view a print you make an assumption of FOV. Two prints of the same size next to each other then you assume similar FOV's which affects your assumptions of scale and distance when you view. It's easy to demonstrate with the same photo, perspective does't really change but you assumptions of the size and distance away the objects are does:













markjwyatt said:


> Ysarex said:
> 
> 
> > ...that means sensor size is a determinant factor for DOF...Joe
> ...



You are correct, see my first, and the second, post on this thread. Because of the nature of the relationships of f-stop, focal length and sensor size it is possible of fix some as constant and therefore cancel others out of the equation. If you hold total light as constant then FOV and aperture diameter are constant. If this condition is set then dof *must* also be constant between equivalent photos. But to achieve this exposure *must also* be different between equivalent photos. If you hold exposure as constant then dof *must vary* between photos.

The trouble is that if you cancel focal length from the equation you *must also* ignore a fundamental relationship between real world sensor size, available f-stops and achievable dof. I've tried to express it in the diagram below, but don't know if it's understandable. What it tries to show is why the 35mm film format is unique. It's easier to understand if you assume *hand held* photography, or photography with a non-static subject, deep dof being easy to achieve to the left of the line:


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## Tim Tucker 2 (Nov 21, 2018)

markjwyatt said:


> I was always taught with portraits that the key is to have the catch light in the eyes sharp. Get that and the impression of sharpness is favorable. Lose that and you lose the image. In your image, the catch light is pretty sharp.
> 
> Here is a picture I took of my dog. I really did not get the catch lights perfectly sharp, and there is an impression of softness (I still like the image but would prefer the eyes to be sharper). If you look closely, the collar is pretty sharp.



Absolutely. Eyes have a natural moisture that acts as a reflector of light, eyes therefore have a higher acutance and we simply expect them to look sharper in a photograph because they always do in the real world, and we always notice the eyes. If you compare my image against yours you will see that they have similar dof, but one you perceive as sharp and the other as soft. It is especially true in portraits that the actual point of focus is more critical than dof and does affect you assumption of sharpness when viewing a print.


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## zulu42 (Nov 21, 2018)

I have to admit I love it when people post misinformation here. Just love it. The resulting education is priceless. Long live TAP!


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## markjwyatt (Nov 21, 2018)

Ysarex said:


> ...
> 
> Be careful with that thinking. This is a case of cause and effect and correlation being very closely related. It can matter at some point that you have the cause/effect relationship straight. Perspective is the rendering of the relationship of objects in 3D space. It is only determined by camera position. We get a chicken/egg thing happen here with very long and short lenses. A long lens is only good for photographing distant objects and so we render those distant objects with what appears to be compressed perspective. Is that a function of the lens or a function of the camera subject distance? We normally use long lenses to photograph far away objects but is the compressed perspective due to the lens or due to the fact that we're far away? It's not the lens it's our physical distance from the subject -- our 3d relationship with the other objects in 3d space.
> 
> Joe



This does make sense given that for instance for an 8x10 format, a "normal lens" is 300-350mm which for 35mm format (again for instance) is a pretty long telephoto.


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## Ysarex (Nov 21, 2018)

Tim Tucker 2 said:


> To be a little more precise, *perspective is entirely from the position of the observer*.
> 
> It is a *chicken and egg* as what is actually happening is easy to mis-interpret if you only try to define it by how a lens works. Focal length has no effect on perspective, it is entirely dependant on the camera position. *But*...
> 
> Perspective is also dependant on the distance you view the print. Though because your eye presents you with a consistent view of the world, one where distances are constant and understood perspective doesn't really change as you change your position to a print. It's not a linear relationship and another demonstration that relationships in images are not defined entirely from the lens but also from our human perception when we view the images. It is why standard lenses are called *standard*, because they present a natural perspective, or the same perspective when we view the print. If you view a print from the same relative position as the camera we see the perspective from the camera position (standard lens for the format), if you view a print from a position that's not the same relative to the camera position you see a distortion of perspective.



Tim, I like the *But...* this has long been a topic of interest for me. It begs the question, how do we present an image such that the viewer experiences as faithful a rendition as possible to what we experienced when taking the photo. And that begs the question of why a standard or normal lens is normal. It's taken on faith (possibly a mistake in this business) that a normal lens presents a natural perspective. You hear, a normal lens mimics human vision, or the normal lens sees the scene the way you do, etc. Apart from just empirically testing that, (in most cases with the scene photographed no longer available), what's the criteria for assigning "normal" to a lens focal length for a given format? The answer that a lens is normal if it's focal length matches the diagonal measure of the film/sensor never sounded to me like an adequate answer if achieving natural perspective was the goal.

So this should interest you: Leslie Stroebel was likewise interested in this question and added some additional information for us to consider. It's obviously limited but what he did was measure an average viewing distance that people naturally stood back to view displayed images. Given the freedom in a gallery to view an image from a distance of choice he was able to say that people on average preferred to view an image from a distance equal to twice the long side of the image. So viewing an 8 x 10 print = 20 inches, viewing a 16 x 20 print = 40 inches, etc. That gives us a number to plug into an equation, and if we run that math the answer is that a normal lens as determined by the film/sensor diagonal comes up a little short.

So by conventional determination a normal lens for a 35mm camera is 43mm (we round up to 50). Using what I'll call the Stroebel method a normal lens for a 35mm is 70mm. I've long had this fantasy that I'd mount a 75mm f/1.4 Summilux on an M4 and live happily ever after.

Joe


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## markjwyatt (Nov 21, 2018)

Ysarex said:


> ...So this should interest you: Leslie Stroebel w...
> 
> Joe



I just got this book from Amazon and look forward to digging into it: _Photographic Materials and Processes_

As an aside, you stated, "how do we present an image such that the viewer experiences as faithful a rendition as possible to what we experienced when taking the photo", is this the "standard for photography" (I think it is one standard, but maybe not the only one). I proposed a group on Photrio, which was not well received: PHOTRIO.COM

I also picked up the domain name http://Standards.photography , currently empty, but...


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## Ysarex (Nov 21, 2018)

markjwyatt said:


> Ysarex said:
> 
> 
> > ...So this should interest you: Leslie Stroebel w...
> ...


Leslie Stroebel is the best.



markjwyatt said:


> As an aside, you stated, "how do we present an image such that the viewer experiences as faithful a rendition as possible to what we experienced when taking the photo", is this the "standard for photography"



Not at all, but it is a unique opportunity for photography and I think worth exploring. Just like it's really good that we have lots of different camera types to chose from there is richness in diversity and there are lots of different ways to approach and practice photography.

Joe



markjwyatt said:


> (I think it is one standard, but maybe not the only one). I proposed a group on Photrio, which was not well received: PHOTRIO.COM
> 
> I also picked up the domain name http://Standards.photography , currently empty, but...


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## john.margetts (Nov 21, 2018)

Ysarex said:


> It begs the question, how do we present an image such that the viewer experiences as faithful a rendition as possible to what we experienced when taking the photo.
> Joe


I think that I can safely say that none of my photographs are faithful renditions of what I see. I am more interested in conveying smell (usually musty), temperature (usually cold), age (usually ancient) and other non visual aspects of my subject (mediaeval churches). Lenses pay only a small part in this.

(I do note that Joe says 'experienced' in the quote above rather than saw. I am really commenting on the desire for faithful which I (and many other photographers) do not share)



Sent from my 8070 using Tapatalk


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## Tim Tucker 2 (Nov 21, 2018)

Ysarex said:


> So this should interest you: Leslie Stroebel was likewise interested in this question and added some additional information for us to consider.



Thanks, just ordered his book on visual principles to take a look, promises to be interesting.



Ysarex said:


> Given the freedom in a gallery to view an image from a distance of choice he was able to say that people on average preferred to view an image from a distance equal to twice the long side of the image. So viewing an 8 x 10 print = 20 inches, viewing a 16 x 20 print = 40 inches, etc.



Though I don't doubt this....



Ysarex said:


> That gives us a number to plug into an equation,



I do question this. You can't equate human vision to equations that easily.

The best illustration I can think of is the 3D pavement art. As you walk around it then you have a fairly consistent view of what you see, until you reach the exact point at which the perspective is designed to create the illusion. At that point your *understanding* or interpretation of the visual cues changes dramatically and you see the 3D effect. It is much the same with images, in that your view of them will be fairly consistent until you stand at a point that coincides with the camera position and a different reality is presented. This different interpretation then takes over as being more consistent with what you understand through experience and therefore the one you brain registers as *the truth*. It is not a gradual process but a more sudden one as your brain is also trying to maintain a *consistent* understanding of what you see. For instance you do not see a world in motion as you drive down the *freeway* but understand a static world and yourself moving through it. It's quite a computation of the absolute reality that your eyes *see*.

_EDIT_: For the diagonal I agree, I don't think that it's actually based on anything other than observation and a useful coincidence.

This is further compounded because we *learn* through experience. As photographers we learn the effects of wide angle lenses and so recognise them more readily than someone who has never seen a photograph. As photographers our interpretation of the image will have a grounding in out experience of learning to see through a camera whereas the non-photo aware eyes will base understanding on reality alone. It is a very real truth in photography that we teach ourselves to view images in terms of our understanding of the photographic process alone.


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## Ysarex (Nov 21, 2018)

Tim Tucker 2 said:


> Ysarex said:
> 
> 
> > So this should interest you: Leslie Stroebel was likewise interested in this question and added some additional information for us to consider.
> ...



I made no such suggestion -- just that Leslie's observation gives us a hard number. Further below you agree the use of the format diagonal isn't especially meaningful. So otherwise we have nothing but repeated empirical observation. We know as you pointed out that perspective is also dependent on print viewing distance. What is or should that distance be -- a normal distance? If we have an average distance that applies to most viewers we can back calculate the lens focal length required to match the FOV to the print. It is then fair to say that if you view a 16 x 20 inch print from 40 inches you will be in the correct position to experience perspective as it appeared from the camera position using a 70mm lens on a 35mm camera. It's also fair to say that if you stay at that 40 inch distance and are presented a 16 x 20 image taken with a 20mm lens on a 35mm camera you're likely to experience the image as distorted, but not necessarily as it's actually pretty easy to fool your brain about what it's seeing.

The numbers along with understanding are useful tools.

Joe



Ysarex said:


> The best illustration I can think of is the 3D pavement art. As you walk around it then you have a fairly consistent view of what you see, until you reach the exact point at which the perspective is designed to create the illusion. At that point your *understanding* or interpretation of the visual cues changes dramatically and you see the 3D effect. It is much the same with images, in that your view of them will be fairly consistent until you stand at a point that coincides with the camera position and a different reality is presented. This different interpretation then takes over as being more consistent with what you understand through experience and therefore the one you brain registers as *the truth*. It is not a gradual process but a more sudden one as your brain is also trying to maintain a *consistent* understanding of what you see. For instance you do not see a world in motion as you drive down the *freeway* but understand a static world and yourself moving through it. It's quite a computation of the absolute reality that your eyes *see*.
> 
> _EDIT_: For the diagonal I agree, I don't think that it's actually based on anything other than observation and a useful coincidence.
> 
> This is further compounded because we *learn* through experience. As photographers we learn the effects of wide angle lenses and so recognise them more readily than someone who has never seen a photograph. As photographers our interpretation of the image will have a grounding in out experience of learning to see through a camera whereas the non-photo aware eyes will base understanding on reality alone. It is a very real truth in photography that we teach ourselves to view images in terms of our understanding of the photographic process alone.


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## Tim Tucker 2 (Nov 22, 2018)

Ysarex said:


> I made no such suggestion -- just that Leslie's observation gives us a hard number. Further below you agree the use of the format diagonal isn't especially meaningful. So otherwise we have nothing but repeated empirical observation. We know as you pointed out that perspective is also dependent on print viewing distance. What is or should that distance be -- a normal distance? If we have an average distance that applies to most viewers we can back calculate the lens focal length required to match the FOV to the print. It is then fair to say that if you view a 16 x 20 inch print from 40 inches you will be in the correct position to experience perspective as it appeared from the camera position using a 70mm lens on a 35mm camera. It's also fair to say that if you stay at that 40 inch distance and are presented a 16 x 20 image taken with a 20mm lens on a 35mm camera you're likely to experience the image as distorted, but not necessarily as it's actually pretty easy to fool your brain about what it's seeing.
> 
> The numbers along with understanding are useful tools.
> 
> Joe



We've gone well off topic here, but it's interesting so I'll throw one more thought into the mix:

What if perspective only exists in a 2D representation of an object?

It's not as weird as it at first sounds. It's just as photographers we automatically assume that what we capture is a representation of a 3D object and therefore how we interpret a picture on a 2D plane is the same as how we see and interpret the actual object in 3D.

What if that wasn't true?

It is very difficult to demonstrate on a computer screen because everything I show you will be a 2D representation and will therefore be seen as a 2D representation. Here's a little experiment you can do with your hands, with palm facing you hold them in front of your eyes with one at arms length and the other about half way but do it so they don't overlap. They look of a very similar size.

Now move them together so they overlap. It's called consistency scaling, you understand that both your hands are the same size and so your interpretation of them will try to be of the same size until they overlap. At which point the illusion is destroyed and you see them in relation to each other and the difference in size becomes apparent.

The camera though will always present a literal recording free of human perceptive effects on a 2D surface through monocular vision. You may at first glance try to see them the same size, but in a static flat 2D rendition of monocular vision you allow yourself to compare actual scaling because you allow the introduction of imaginary *vanishing points* that are just converging lines on a 2D surface.

Here is another:






On the left is either an oval or a circle, it's ambiguous in a 2D representation. On the right you clearly see it as a circle within a rectangle. Think about this for a second, if you understand it as a rectangle then you understand and see it to have parallel sides so your human perception in the real 3D world has no vanishing point. It's only when I represent it in 2D that the vanishing point becomes clear, that you see clearly how a 3D object is represented in 2D space. I've added something in a 2D space that clearly influences your interpretation of what you see and makes you equate it to a 3D object. The reality is that it is an oval in a rhomboid on a 2D surface yet you don't interpret the reality, you see the illusion.

Artists used to do it by either tracing lines on a sheet of glass or through use of a camera obscura. Vanishing points and perspective only become visible in 2D representations, in the 3D representation you eye/brain is doing as much as it can to subtract or cancel perspective in order to allow you a consistent view as you walk through the landscape. One where objects maintain a consistent size and distance relative to each other, one where they don't change relative to your position.

I can distort our rectangle and circle in many ways by moving the imaginary vanishing point around, from the Degas style of *off the page* to one with a virtual horizon on the page:





It still looks like a circle in a rectangle. But ask yourself if it were a real 3D object do vanishing points move as you walk around the object? How dizzy would you get if they did?

Here's another. Imagine yourself walking past a 2D image, is the perspective or vanishing point actually fixed or is it entirely dependant on the position of the observer?





In this 2D representation there is a clear indication of a vanishing point towards the middle of the frame. But if we move to the right then the implied vanishing point moves off the left of the frame:





And yet your impression is that you are still standing directly in front of the chair. If you walked past the subject then your impression would be entirely different, that the objects are static and their edges parallel.

2D representations clearly do not behave in the same way as real 3D objects. This begs the question of whether trying to understand the 3D world in terms of how perspective works in a 2D image is preventing you from understanding how we actually see the real 3D world? Perhaps there is no real correlation between how we create the illusion of depth in a 2D image and we interpret the 3D world. Perhaps 2D images will always be a distortion and never a representation, that we only see them as representative because the *hypothesis generator* in our brains equates them to the view we are most familiar with - reality. In images we create an illusion of reality, not reality itself. Illusions work because we do not see them properly not because they are an accurate representation of reality. Even tilting the camera and displaying the image vertically distorts your perception...

Renaissance perspective actually has five elements, linear perspective is but one. Trying to understand 2D images by only linear perspective is also trying to limit understanding into a rationalisation that is already understood and fails to recognise anything outside what is understood.


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## Designer (Nov 22, 2018)

Speaking of 3D perception of a 2D object:

(Scroll to 7:23.)


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## Tim Tucker 2 (Nov 22, 2018)

Designer said:


> Speaking of 3D perception of a 2D object:



The illusion actually works in 3D as well. It's because you make the assumption that best fits your experience, that the head is a positive fold rather than negative. It highlights that a lot of what we see isn't so much real but the interpretation that makes to most realistic sense to us, the one that's most consistent to our experience and learning.


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## ORourkeK (Nov 28, 2018)

Well, this has been a blast to read. Sure have missed this site. Thanks for the entertainment, all.


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