# Fullframe lenses - softer on crop sensor bodies



## Overread (Mar 5, 2016)

Videos like this make me wish I invested more time into learning about the math/theory behind photography more. Sure it won't (well might not - chances are it won't) make me a better artist; but still it makes me wish I knew more because what this video says (by some random guy in the world on the net) goes against - well - most of what seems to make sense. 



So what are your views; anyone got enough math/photography understanding to really understand this ? (


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## Derrel (Mar 5, 2016)

Sooooooo tired of this B.S. about light gathering...utter BS...this is a NEW line of "logic" that really is not accurate. F/2.8 is ALWAYS f/2.8...the idea that f/2.8 on APS-C somehow becomes light gathering that is in effect only F/4.2 is...a common internet myth that has arisen within the last two years.

The idea that light-gathering is a relative property, dependent upon a large sensor gathering "more liught" and a smaller sensor gathering "less light" is false logic. Again--this is a cock-and-bull story that has only recently begun making the rounds on the internet.

We can NOT attempt to use relative capture size as a determinant in how much light is gathered! IT DOES NOT WORK THAT WAY AND HE IS FULL OF CRAP!

Take a 4x5 sheet of film. Take a 6x9 centimeter frame of roll film. Take a 6x6 centimeter frame of of rollfilm. Take a 6 x 4.5 centimeter rectangle of rollfilm. Take a 24x36mm frame of 135 format film. Go outside on a BRIGHT,sunlighted day and use the same film in every camera: T-Max 400. Set the shutter to 1/400 second and f/16.

At f/16 and 1/400 second, the exposure will be correct for EVERY CAPTURE SIZE!!! My Gaaaaawd....exposure has NOTHING to do with the area of the capture medium: this is brand-new, Internet-era B.S..


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## Derrel (Mar 5, 2016)

Yes, depth of field changes with capture size. Smaller formats have inherently deeper DOF per angle of view. But the idea that an f/2.8 lens shot wide open at f/2.8 when mounted on a small-sensor "captures less light"  than it does when used on a larger sensor, like FF, is a fallacy. Extending TOny's B.S. line of "talking", by the same token, that f/2.8 lens when used on a 645 rollfilm camera would magically become  what? An f/2.o lens? And if used on a 6x9 rollfilm camera, that f/2.8 lens would become what? A Unicorn and Fairie Fart f/1.4. Right?

JFC...this guy...


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## Didereaux (Mar 5, 2016)

Overread said:


> Videos like this make me wish I invested more time into learning about the math/theory behind photography more. Sure it won't (well might not - chances are it won't) make me a better artist; but still it makes me wish I knew more because what this video says (by some random guy in the world on the net) goes against - well - most of what seems to make sense.
> 
> 
> 
> So what are your views; anyone got enough math/photography understanding to really understand this ? (




Any lens on a crop body actually improves the image(sensor quality being equal).  Crop sensors do not take in the corners where vignetting and other distortions normally occur!


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## snowbear (Mar 5, 2016)

I just did a quick, semi-scientific test:
Lens: AF 24mm f/2.8 D Nikkor (full frame).
Camera 1: Nikon F90s (35mm  film = full frame)
Camera 2: Nikon D40 (1.5 Crop sensor)

Both cameras set to ISO 400; lens set to f/2.8 (direct set on the N90s, via the body's aperture control on the D40)
Both cameras set to spot metering.
Both cameras aimed at a ceiling lamp in the next room.

Camera 1's meter centered out at 1/1000.  Camera 2's meter centered out at . . . wait for it . . . 1/1000.
Observation says the aperture is the same on both cameras.  Conclusion: You-tube talking head is fos.


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## Didereaux (Mar 5, 2016)

Overread said:


> Videos like this make me wish I invested more time into learning about the math/theory behind photography more. Sure it won't (well might not - chances are it won't) make me a better artist; but still it makes me wish I knew more because what this video says (by some random guy in the world on the net) goes against - well - most of what seems to make sense.
> 
> 
> 
> So what are your views; anyone got enough math/photography understanding to really understand this ? (




Tony Northrup is only a photographer in his own mind.  He has built a career selling his borrowed and re-phrased garbage to gullible, lazy neophytes who never check anything beyond Northrup....and then refer their friends to him.  Ought ot be hog-tied and dipped in a vat of developer....for a week!    Out side of that I have no strong opinions on the guy!


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## xenskhe (Mar 5, 2016)

(casually) "I have a friend, he's a genius" lol.
What's that blueprint poster in the background?  Looks like an old 'bullseye' camera.


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## snowbear (Mar 5, 2016)

Didereaux said:


> Tony Northrup is only a photographer in his own mind.  He has built a career selling his borrowed and re-phrased garbage to gullible, lazy neophytes who never check anything beyond Northrup....and then refer their friends to him.  Ought ot be hog-tied and dipped in a vat of developer....for a week!    Out side of that I have no strong opinions on the guy!



Placed in locked windowless room with that Rock-wall guy?


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## xenskhe (Mar 5, 2016)

Didereaux said:


> Crop sensors do not take in the corners where vignetting and other distortions normally occur!



Exactly, and as he's already stated, the greater DOF; which presumably includes sharper _surroundings._


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## Ysarex (Mar 5, 2016)

Derrel said:


> Sooooooo tired of this B.S. about light gathering...utter BS...this is a NEW line of "logic" that really is not accurate. F/2.8 is ALWAYS f/2.8...the idea that f/2.8 on APS-C somehow becomes light gathering that is in effect only F/4.2 is...a common internet myth that has arisen within the last two years.
> 
> The idea that light-gathering is a relative property, dependent upon a large sensor gathering "more liught" and a smaller sensor gathering "less light" is false logic. Again--this is a cock-and-bull story that has only recently begun making the rounds on the internet.
> 
> ...



The people making this argument are trying to use "total light gathered" and crop factors as another format "equivalence" function and in this case pertaining to noise. They're claiming that noise comparisons APS versus FF can be made equivalent by applying the crop factor to total light gathered which can then be expressed hand in hand with the DOF equivalence by focusing on the lens f/stop. In other words the APS image (correct exposure at f/2.8) is noisier than the FF image by the amount you would see if you under-exposed the FF sensor to the same scene at f/4.2 when correct exposure was f/2.8. And, Oh great wonder, the DOF would be the same as well. "I'm so damn clever I'm going to make a Youtube!"

It is true that smaller sensors are inherently noisier than larger sensors: (Clarkvision: Does Pixel Size Matter) because the smaller photosites (pixels) on the smaller sensors gather less light, *but this equivalence rubbish expressed as an f/stop variance in the lens is bleepin' nonsense.* It's far too complex for the likes of Tony's feeble mind to keep straight and express coherently.

I'm 100% behind Derrel on this one: f/2.8 is f/2.8 is f/2.8 no matter what the lens and camera. The lens f/stop doesn't change when you switch bodies. This whole bleep bleep "equivalence" nonsense needs to stop. It's not helpful. For 30 years I shot film cameras from 8x10 sheet all the way down to 35mm and was often working with 2 and 3 formats at the same time. I never once asked myself, how is this Nikon equivalent to this Rollei? Well in order to get the same shallow DOF with my Nikon that I get with my Rollei my Nikon 105mm f/2.5 is really a 150mm f/4.8 -- never did that. These people have a problem.

Joe


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## nerwin (Mar 5, 2016)

I think people are getting way too technical these days. 

*Just shoot.*


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## xenskhe (Mar 6, 2016)

nerwin said:


> *Just shoot.*


 ..film.


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## Overread (Mar 6, 2016)

What I love is he spends the first part of the video saying that you get sharper and more detailed photos from crop lenses on fullframe bodies; then flips it around and says "ahh but for wildlife its the other way around because - er because....."


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## Tim Tucker (Mar 6, 2016)

Ysarex said:


> I'm 100% behind Derrel on this one: f/2.8 is f/2.8 is f/2.8 no matter what the lens and camera. The lens f/stop doesn't change when you switch bodies. This whole bleep bleep "equivalence" nonsense needs to stop. It's not helpful. For 30 years I shot film cameras from 8x10 sheet all the way down to 35mm and was often working with 2 and 3 formats at the same time. I never once asked myself, how is this Nikon equivalent to this Rollei? Well in order to get the same shallow DOF with my Nikon that I get with my Rollei my Nikon 105mm f/2.5 is really a 150mm f/4.8 -- never did that. These people have a problem.
> 
> Joe



Absolutely.  Equivalence is just a way of comparing noise performance between sensors. But given that most noise in photographs comes from under-exposure rather than sensor performance it's a fairly pointless thing to learn.

f-stop is simply the ratio between the aperture diameter and the focal length. A 200mm lens at f4, or 1:4 has an effective aperture diameter of 50mm (50:200 - 1:4). A 50mm at f4 has an effective aperture diameter of 12.5mm. This is the same for all 50mm lenses and doesn't change regardless of what format you put it on. Lenses for the larger formats are just designed to give a bigger coverage (project light from a wider field of view onto a larger sensor). This is not 'wasted light' in a smaller sensor because it comes from objects that the sensor can't 'see'.
Because of the beautiful balance this system's designed to have a 200mm lens at f4 (50mm diameter aperture and focussing light from a much smaller field of view) actually projects the same amount of light per sq mm as a 50mm lens at f4 (12.5mm) that focusses light from a much larger field of view.

The f-stops are so constant and in-variable they're printed on the sides of the lenses.

Now why somebody should want to buy a lens for their crop factor camera, set an aperture that's an exact ratio of it's diameter to it's focal length and then express that ratio as the number they would've had to use to get the same dof in a camera they don't have, is beyond my tiny mind. 

I also couldn't help noticing that when you use ff lenses on crop sensors they're softer because of something called perceptual MP (???!!!), unless you shoot wildlife in which case we use actual camera MP and the ff lenses are sharper.


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## Overread (Mar 6, 2016)

I suppose the long lens thing is that Tony doesn't want to try and argue that the various 70-300mm crop lenses are sharper than the supertelephoto lenses - when used on crop bodies. Even though the latter are all fullframe lenses


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## astroNikon (Mar 6, 2016)

Didereaux said:


> Overread said:
> 
> 
> > Videos like this make me wish I invested more time into learning about the math/theory behind photography more. Sure it won't (well might not - chances are it won't) make me a better artist; but still it makes me wish I knew more because what this video says (by some random guy in the world on the net) goes against - well - most of what seems to make sense.
> ...


Yeah, but if your landscape photo doesn't contain the "edges" that you want to include, then you'll have to use an even wider lens on the crop body, thus reintroducing your distortions, generally speaking.

If you want your FF image to only contain the inner part like an APS-C image, then you can also crop it which will remove the edges.

This is an argument of using different FOV and using less or more of the projected lens image.
You have to compare the same image on both sensors for a proper evaluation which may mean different lenses.

Lens quality has a lot to do with it too.
from this forum the 18-55s seem really sharp.  But the nikon 55-200s are just soft from the couple I've tried.


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## nerwin (Mar 6, 2016)

See I always thought that full frame lenses are sharper corner to corner on crop bodies because you are using the center portion of the lens.


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## Bebulamar (Mar 6, 2016)

Overread said:


> Videos like this make me wish I invested more time into learning about the math/theory behind photography more. Sure it won't (well might not - chances are it won't) make me a better artist; but still it makes me wish I knew more because what this video says (by some random guy in the world on the net) goes against - well - most of what seems to make sense.
> 
> 
> 
> So what are your views; anyone got enough math/photography understanding to really understand this ? (



Yes I understood what he said and he was correct. When I first watched Tony I didn't like him because he sounded like a bragger. But I found him very good technically although his art may be not all that good.


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## Ysarex (Mar 6, 2016)

Bebulamar said:


> Overread said:
> 
> 
> > Videos like this make me wish I invested more time into learning about the math/theory behind photography more. Sure it won't (well might not - chances are it won't) make me a better artist; but still it makes me wish I knew more because what this video says (by some random guy in the world on the net) goes against - well - most of what seems to make sense.
> ...








Tony: "Take a full frame 24-70 f/2.8 lens. This is one of the most common lenses I see people using on crop bodies. If you put it on a Nikon or Sony APS-C body with a 1.5x crop, it behaves exactly like a 36-105mm f/4.2 full frame lens would on a full frame body."

*That statement is technically incorrect.* At the same ISO the APS-C camera using the 24-70 f/2.8 lens wide open would achieve correct exposure with a stop and a third faster shutter speed than the full frame camera using a 36-105 f/4.2 lens wide open. Tony is confused.

Joe


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## Bebulamar (Mar 6, 2016)

I just made my answer to the OP. I make no arguement because it's clear that nobody agreed with Tony. So if he can't convince you how can I.


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## Ysarex (Mar 6, 2016)

Bebulamar said:


> I just made my answer to the OP. I make no arguement because it's clear that nobody agreed with Tony. So if he can't convince you how can I.



You're not Tony. You might be able to talk logically about photography with a solid understanding of how it works.

I'm not just disagreeing with him. I'm calling him wrong and providing clear facts that prove he's wrong. I believe I just did that.

Joe


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## Dave442 (Mar 6, 2016)

I think Tony should stop calculating physical lens properties using "equivalent" focal lengths. We didn't physically change the focal length of the lens so we can't use that crop-factor focal length in the calculation of the f-stop.

If Tony took his handheld light meter and read the scene at 1/500 and f/5.6, it does not matter whether he is using a 200mm lens on a crop body or a 300mm lens on a full frame camera, he needs  to use that same exposure. He can't use a 300mm lens at f/8.4 on the full frame body and get the same exposure as he did with the 200mm at f/5.6 on the crop body. But, this is also why we shouldn't go around saying that we took the shot at 300mm when it was actually taken using a 200mm on the crop body.

Whatever parts in the scene that have the correct exposure at 1/500 at f/5.6 are going to be properly exposed no matter what lens and camera combination is used to record it, that was the main reason to have an f-stop.


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## Braineack (Mar 7, 2016)

I blame Tony Northrup.  All this drivel started with him.

He's the one that started this aperture equivalence drivel. While he is technically correct -- He purposefully ignores the point that it only effects DOF.  If you watch he comparisons, he changes the ISO in shots between sensor sizes to keep the exposure equal.

Here's a screen grab from one of his videos explaining the concept:




It's all because of him.  He even goes as far as, in the above video, to say that the micro 4/3 has better IQ than the FX because it's being shot at a lower ISO.

He's doing it to spark controversy and confusion and drive views to his videos/blog.


How he calculates the difference in DOF between the two is, however, pretty accurate.  Shooting f/2.8 on a small sensor, will be like shooting stopped down on a FX.


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## Overread (Mar 7, 2016)

Thing is Ken Rockwell did a similar thing, only he tended to use more extreme opinions rather than pure calculated fact; indeed a good few even like his technical reviews for the technical content; ignoring or glossing over the Rockwellian opinions. 

This Tony chap seems to be really pushing false information and sadly it will only cause a world of confusion. Heck considering how in the same video he even confuses the issue by talking up how you should use crop sensor lenses only on crop sensor cameras and then flips it over to say for wildlife its different.

I suspect the fact that canon only has 9 or so crop sensor only lenses might also influence his viewpoint.


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## JacaRanda (Mar 7, 2016)

How many clicks did he just get?


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## Overread (Mar 7, 2016)

Not enough probably 

That said hopefully he gets enough attention that enough bigger names can - counter or knock him down. 

It's one thing to be opinionated; heck many a website had a quip about Ken and his hate of tripods on it; however this is different. Tis a shame because all it will do is REALLY confuse newbies


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## astroNikon (Mar 7, 2016)

So .. if I use electrical tape and mask out the outer edge of my FF lens, will the image be sharper on my crop camera ?


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## robbins.photo (Mar 7, 2016)

astroNikon said:


> So .. if I use electrical tape and mask out the outer edge of my FF lens, will the image be sharper on my crop camera ?



Yes, but only if your shooting wildlife apparently.  If your shooting anything else, well that changes the math.. er.. somehow.


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## Tim Tucker (Mar 8, 2016)

Bebulamar said:


> I just made my answer to the OP. I make no arguement because it's clear that nobody agreed with Tony. So if he can't convince you how can I.



Ah, but there is a basic mis-conception in 'equivalent f-stop' and that is that it is not a measure of dof and never has been.

Dof is a highly perceptual 'rule of thumb' regarding apparent sharpness in prints when viewed at a certain magnification at a certain distance. But:
a) the subject matter and the way it's lit can have a greater impact of apparent sharpness than the 'crop factor'.
b) it fails to take into account lens design and lens aberrations some of which are deliberately designed into lenses, (how do you work out the equivalent f-stop between a sigma art and a pretzel?).
Also the whole thing falls flat when you view a digital image on a screen because:
a) if you view it as a whole image it requires a re-size with will re-calculate the value of every pixel in the image and the acutance of every edge.
b) if you view it at 100% the perception of sharpness is gone.

The f-stop is the precise mathematical relationship between the effective diameter of the aperture and the focal length of the lens. It's constant is the theoretical transmission of light per sq mm, it is not and never has been a measure of dof. Dof is affected by changes in, format size, aperture, focal length and distance from the subject. To calculate dof you need to know all of these, you cannot calculate dof by aperture alone.

If you stop thinking of photography as the limited formats of digital and start thinking in terms of the vast differences in formats of film then the whole equivalent dof becomes meaningless. For instance how does it work between a 10"x 8" print from a 35mm negative and a contact print from 10"x 8" sheet film when the enlargement (magnification) of the film is such a large part of perceived sharpness (dof)?

Besides if you use dof equivalence as a guide for f-stop then it follows that you must then use sensor size as part of your exposure calculation when the determination for exposure is light per sq mm.


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## Braineack (Mar 8, 2016)

Tim Tucker said:


> Besides if you use dof equivalence as a guide for f-stop then it follows that you must then use sensor size as part of your exposure calculation when the determination for exposure is light per sq mm.



I actually like his formula.  It lets someone know when shooting a pea-shooter 1" sensor, that even at f/2.8, they're going to end up with a background blur more in line with a full-frame at ~f/8.

It's a pretty good rule of thumb that actually does work.


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## Tim Tucker (Mar 8, 2016)

Braineack said:


> Tim Tucker said:
> 
> 
> > Besides if you use dof equivalence as a guide for f-stop then it follows that you must then use sensor size as part of your exposure calculation when the determination for exposure is light per sq mm.
> ...



I don't doubt that it works, but then there are a lot of very symmetrical relationships in the whole system. I just don't see how ff suddenly became the benchmark, the constant used to be f-stop and now it's ff to which things are equivalent. What if you don't have a ff camera and have no experience with one how does the comparison help there? 

Ignoring the enlargement factor  you could say that all 50mm lenses at f2.8 have the same dof characteristics regardless of format. There's a constant right there that doesn't distort the f-stop, and also makes the dof indicator scales on my MF Nikkors quite handy.


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## Braineack (Mar 8, 2016)

oh yeah, Tony completely ignore everything else, there's no doubt about that.

in the video in post #1, he ignores that the simple fact that a smaller sensor simply cannot resolve the same level of "P-sharpness" than a larger one and doesn't factor that in.

Notice is his first example, the soft 24-70 he uses resolves at 14/22MP on FF, and only 7/18MP on a crop.  So right off the back there's a loss of 37% sharpness on a FF sensor, but there's a loss of 62% potential sharpness on the 7D.  a 25% difference in sharpness just between the two image sensors.

With that said, yeah, there may be some crop lenses that may be sharper than some full-frame lenses on a crop body, but it's not because you're "focusing all that light onto the sensor itself" verses "digitally zooming light".

His friend sent the lens into Canon, because it's a crap soft lens that will be soft on any camera.


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## astroNikon (Mar 8, 2016)

Tim Tucker said:


> I don't doubt that it works, but then there are a lot of very symmetrical relationships in the whole system. I just don't see how ff suddenly became the benchmark, the constant used to be f-stop and now it's ff to which things are equivalent. What if you don't have a ff camera and have no experience with one how does the comparison help there?
> 
> Ignoring the enlargement factor  you could say that all 50mm lenses at f2.8 have the same dof characteristics regardless of format. There's a constant right there that doesn't distort the f-stop, and also makes the dof indicator scales on my MF Nikkors quite handy.



I never really understood the crop factor thing with lenses UNTIL I bought a FF camera.
THEN it all made sense.
So using a FF sensor which creates a 1:1 mathematical model with the lens designed for a FF (35 mm film) makes sense to use it as the benchmark.


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## Overread (Mar 8, 2016)

Fullframe/35mm film is only the common benchmark because in the pre-digital era it was the most common film size. Most disposable cameras and many SLRs and other formats were 35mm. Thus the average Joe likely had experience of the 35mm format to the point where when digital first came out it got the name "crop" because its sensor size was smaller than the more common 35mm; even though during the film era there were a huge number of different format sizes.

The only reason the whole conversion thing even exists is mostly because of those who have 35mm film experience coming into the digital world. Today its a null point; most new to photography are entering with digital and this might never touch a 35mm sensor; meanwhile those who do want to shoot with a fullframe camera have affordable new and secondhand options on the market to pick from so they don't have to worry about using a crop camera. 


Furthermore then and now the medium and large formats are rather luxury and whilst film medium and large format gear can be gotten cheaper than before its still nowhere near mainstream.


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## astroNikon (Mar 8, 2016)

plus the camera manufacturers have been using that as a standard for marking the lenses for at least FF down smaller.  I saw one instance a few years ago with one of the Nikon J or V cameras where the lens was marked with the focal length zoom AND the equivalent focal length.


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## Overread (Mar 8, 2016)

Aye heck most point and shoots mark equivalents in 35mm focal length on their lenses


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## Derrel (Mar 8, 2016)

dPreview's September 2012 article, "*Background blur and its relationship to sensor size*"
Background blur and its relationship to sensor size
does a pretty systematic comparison of the common digital sensor sizes.

Focal length used and the resulting angular field of view, format size, aperture value, *all these things, and more*, affect both depth of field AND the degree of background blurring.

This article uses the terms of no blur, very limited blur, limited blur, reasonable blur, strong blur, and very strong blur. These numbers are for a *Portrait Image, with an image height of 0.6 meters*--so, comparing the degree of background blurring on an image of the SAME height, despite different sensor sizes and different lens lengths and maximum aperture values.

Check it out!


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## gckless (Mar 9, 2016)

I didn't read many responses, but watched about 2 minutes of the video (what I could stomach), and I had to stop. I hate that he's perpetuating that larger photo size (higher MP count) equates to better photos. Also, I see that the aperture piece has been addressed once or twice...lol.


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## unpopular (Mar 13, 2016)

Derrel said:


> Yes, depth of field changes with capture size..



DOF stays the same also. Working distance changes and this affects focus distance, which gives the impression that DOF changes.

Cropping the image circle doesn't change the lens, only how the lens is used.


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## Braineack (Mar 13, 2016)

unpopular said:


> Derrel said:
> 
> 
> > Yes, depth of field changes with capture size..
> ...


No. You're wrong.  This is why people don't like you.

using tapatalk.


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## Ysarex (Mar 13, 2016)

unpopular said:


> Derrel said:
> 
> 
> > Yes, depth of field changes with capture size..
> ...



DOF does change with capture size. The size of the film or sensor is one of the determinant factors for DOF. You can't calculate DOF without a value for the circle of confusion. The circle of confusion is calculated based on the size of the recording medium. Therefore the size of the recording medium (film/sensor) is a DOF determinant factor.

This is a hard one to clear up. This misconception is very widespread and deeply rooted.

Joe


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## unpopular (Mar 13, 2016)

So if I took a lens, projected the image on the wall and then drew a rectangle out on the wall and labeled it "image area" the depth of field would change within the rectangle?


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## Ysarex (Mar 13, 2016)

unpopular said:


> So if I took a lens, projected the image on the wall and then drew a rectangle out on the wall and labeled it "image area" the depth of field would change within the rectangle?



Not a correct usage of DOF. DOF and how it is calculated is well defined by the industry. I.e. DOF is not calculated at the film plane.

Calculations for DOF require a value for the circle of confusion: Circle of confusion - Wikipedia, the free encyclopedia

As I said, the CoC is calculated based on the size of the film or sensor. Show us the math that says otherwise, otherwise here is a simple proof:




 

Where H = hyper focal distance, f = focal length, N = f stop, and c = circle of confusion. *The formula requires a value for c.*

Reference: Hyperfocal distance - Wikipedia, the free encyclopedia

Joe


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## astroNikon (Mar 13, 2016)

To my understanding, as mentioned, DOF is based on sensor size.

This is totally obvious when you get to smaller sensors. 
My 1/1.7" Nikon P7800 at 50mm has a gigantic DOF at f/2.8 versus the same on a FF.  This is totally obvious.   On a APS-C this may not be totally obvious depending upon the experience of the viewer.

This is also one of the reasons the f/1.8 DX lenses are out there, to provide a similar DOF as the equivalent f/2.8 FF lens for APS-C sensors.


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## unpopular (Mar 13, 2016)

Derrel said:


> f the SAME height, despite different sensor sizes and different lens lengths and maximum aperture values.





Ysarex said:


> unpopular said:
> 
> 
> > So if I took a lens, projected the image on the wall and then drew a rectangle out on the wall and labeled it "image area" the depth of field would change within the rectangle?
> ...



You're absolutely right. And come to think of it, it makes sense.

However, my math is still suggesting that magnification is a significantly greater factor until you get into higher magnifications.


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## Ysarex (Mar 13, 2016)

unpopular said:


> Derrel said:
> 
> 
> > f the SAME height, despite different sensor sizes and different lens lengths and maximum aperture values.
> ...



Oh hey, I didn't say anything about how important a factor sensor size is -- just that it's a factor. Absolutely magnification is the dominant factor in controlling DOF -- you are correct. Reduced to most simple form DOF is a function of magnification and f/stop.  Magnification expands to a fairly complex component of the equation that includes subject distance, focal length and ultimately enlargement. Sensor size plays it's role when you expand the factor enlargement.

Joe


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## Alexr25 (Mar 13, 2016)

unpopular said:


> DOF stays the same also. Working distance changes and this affects focus distance, which gives the impression that DOF changes.


As others have pointed out this assertion is wrong.



unpopular said:


> Cropping the image circle doesn't change the lens, only how the lens is used.


You got this right but your conclusion is wrong because you in common with many people assign depth of field to be a property of the lens. IT IS NOT. Depth of field is a property of human vision.
A lens has only one plane of focus and anything that is not in that plane will to some extent out of focus.
Depth of field is perceived by the viewer because human vision is not perfect and any object that subtends less than approx of 1 minute of arc is perceived as a point. This is why a photo may look sharp printed as a postcard sized image but look horrible when blown up to poster size.
Some people point to the depth of field markings you see on some lenses to argue that DoF is a lens property but those markings assume you will be viewing an 8" x 10" uncropped print of the full image at a distance of 1 foot, at any other print size or viewing distance the perceived depth of field will not match the lens markings.


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## Ysarex (Mar 13, 2016)

Alexr25 said:


> unpopular said:
> 
> 
> > DOF stays the same also. Working distance changes and this affects focus distance, which gives the impression that DOF changes.
> ...



Careful here. You don't want to entirely disassociate the lens (lens focal length) from DOF. Each lens focal length has a unique relationship with DOF and plays a determinant role in calculating DOF. In the math equations that are used to calculate DOF one of the required variables is lens focal length. If the lens doesn't have anything to do with it then it wouldn't be a variable in the math formulas.

Joe



Alexr25 said:


> Depth of field is a property of human vision.
> A lens has only one plane of focus and anything that is not in that plane will to some extent out of focus.
> Depth of field is perceived by the viewer because human vision is not perfect and any object that subtends less than approx of 1 minute of arc is perceived as a point. This is why a photo may look sharp printed as a postcard sized image but look horrible when blown up to poster size.
> Some people point to the depth of field markings you see on some lenses to argue that DoF is a lens property but those markings assume you will be viewing an 8" x 10" uncropped print of the full image at a distance of 1 foot, at any other print size or viewing distance the perceived depth of field will not match the lens markings.


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## Overread (Mar 14, 2016)

If you want a good practical example try macro. The working distances at 1:1 is identical if you use the same lens on crop and fullframe; however the depth of field should be more apparently different when you compare fullframe to crop sensor.


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## astroNikon (Mar 14, 2016)

So ... just to throw some oil on the fire in regards to "magnification"

Does DOF change on an APS-C sensor if it is a 24 megapixel  versus a 6 mpixel sensor of the same area, though highly different pixel density ?


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## Derrel (Mar 14, 2016)

Depth of field is a fairly complex subject. The ***best*** writer on the net, as far as clearly and correctly explaining the issue is Bob Atkins. Period.

Something to keep in mind is that _depth of field_, the area of acceptably sharp focus, _is NOT the same, exact thing as background blur_. Background blur, the magnitude of the blur in the background, increases with the physical SIZE of the lens aperture in an ABSOLUTE sense.  Take a look at the teaching illustration below at the link compare2.jpg. It has three photos, each which show the same depth of field, and each photos has the same object height and width within the picture frame area--but because the lenses used were of different focal lengths, the physical size, the actual width of the aperture opening inside the lens, was progressively larger and larger, and *the longer the lens, the higher the degree/magnitude* of background blurring.

The three photos were all made at f/2.8. The 50mm lens had a 17.8mm aperture width at its f/2.8 setting; the 85mm lens had an aperture width of 30.4mm at its f/2.8 setting; and the 135mm lens had an f/2.8 aperture that measured 48.2mm in width. So, a 50mm, an 85mm, and a 135mm lens, SAME MAGNIFICATION of the target subject, same depth of field region as seen in an actual photo--yet significantly *more background blur the longer the lens length*.

The degree of background blurring is something many people seem fixated on, enthralled by--this is why there are many fashion/portrait/lifestyle shooters who favor LONG focal length and very WIDE-aperture lenses, lenses which have physically very wide actual aperture openings: lenses like the 85mm f/1.2, 135 f/2 and 135mm f/1.4, 200mm f/2, and 300mm f/2.8 and 400mm f/2.8. The magnitude of background blurring is something many people really seem to be concerned with--in some types of photograpy, and Tony Northrup seems especially fixated on it as some type of measuring stick.

Again...*background blur is not the same, exact "thing" as depth of field*. When you want more and ore and more background blurring, the easiest way to get that is to use a longer focal length, one in which the massive lens diameter openings at each f/stop value are significantly larger than with short focal length lenses.

compare2.jpg


^^^^As Bob Atkins wrote in the caption for the above image: "A_s you would expect, at the same magnification, the faster the lens, the smaller the depth of field. This also means that the background close to subject will be blurred more by the faster lens. In this case the 50mm lens at f1.4 gives slightly greater blurring for objects up to about 1m behind the subject in focus. However as you go further back, the lens with the largest physical aperture starts to show the most blur, and by the time you're at infinity, the 135mm lens at f2 lens will give almost twice as much blurring (actually 1.9x as much). The following images show the effect quite clearly. All three were shot to produce the same magnification of the camera box and so have essentially the same depth of field (region of "acceptably sharp" focus), but the image shot with the larger physical aperture (longer focal length) lens shows the greatest degree of background blur_."

Now....we're talking here about the magnitude of the background blurring--not the DOF, but something else. Bob's second article, and his software application bacgroundblur.exe  can be downloaded from this page:  Bokeh and Background Blur Calculator- Bob Atkins Photography


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## DarkShadow (Mar 14, 2016)

All this technical crap gives me a migraine.I like to spend less time  thinking about full frame vs crop or FX vs DX glass and spend more time thinking about shooting and Improving. I am happy as a clam with my D7200 and slow sigma 150-600mm and my slow 18-140 kit lens for general walk around things.


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## Ysarex (Mar 14, 2016)

astroNikon said:


> So ... just to throw some oil on the fire in regards to "magnification"
> 
> Does DOF change on an APS-C sensor if it is a 24 megapixel  versus a 6 mpixel sensor of the same area, though highly different pixel density ?



No.

Joe


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## unpopular (Mar 15, 2016)

Ysarex said:


> astroNikon said:
> 
> 
> > So ... just to throw some oil on the fire in regards to "magnification"
> ...



Now wait!! If you have greater resolution shouldn't the minimum circle size be smaller? If so, wouldn't image resolution present a maximum DOF regardless of viewing resolution????


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## unpopular (Mar 15, 2016)

(or does this only apply at 1:1 enlargements?)


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## Ysarex (Mar 15, 2016)

unpopular said:


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



By minimum circle do you mean circle of confusion? No. Circle of confusion is not a function of the resolution of the recording medium. Think film. Back in the 80s there was a short fad to shoot 35mm recording film -- super high resolution but with a dynamic range of maybe 3 stops. DOF between recording film and Tri-X didn't change because of the res difference. Remember DOF is calculated to a standard output print size. You couldn't make a DOF comparison between Tri-x printed 8x10 with recording film printed 30x40. Same goes for digital today.

Joe


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## unpopular (Mar 16, 2016)

What the _what_?

The circle of confusion has nothing to do with the recording medium nor the enlargement. From Wikipedia:



> 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.



This is how it has always been described to me. What you seem to be referring to is depth of field, or region of "acceptable sharpness". Again, wikipedia:



> The depth of field is the region where the CoC is less than the resolution of the human eye (or of the display medium).



So essentially what you'd have in a theoretically perfect lens is a perfect cone of light being focused onto an infinitely small point on the film plane:




(courtesy Wikipedia, public domain: File:Cirles of confusion lens diagram.png - Wikimedia Commons)

If the circle of confusion as defined is smaller than the resolving power of the system in whole, including [reluctantly] viewing conditions, we can call that area "sharp" or "in focus" because we no longer can see the individual circles being projected.

If this is the case, then certainly the resolving power of the medium must have an impact to some extent. If the film or sensor cannot resolve a circle diameter difference between one working distance and another, provided fixed focal distance, then both distances will be recorded essentially the same when looking at diameter alone and thus nothing about depth.

I'm also having some issue with the concept of "enlargement" with digital photography in regard to sensor size, and I am questioning if you can make the same type of comparisons as you can with film ... but more on that later.


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## Ysarex (Mar 16, 2016)

unpopular said:


> What the _what_?
> 
> The circle of confusion has nothing to do with the recording medium nor the enlargement. From Wikipedia:
> 
> ...




"In photography, the circle of confusion diameter limit (“CoC”) for the final image is often defined as the largest blur spot that will still be perceived by the human eye as a point.

With this definition, the CoC in the original image (the image on the film or electronic sensor) depends on three factors:

Visual acuity. For most people, the closest comfortable viewing distance, termed the _near distance for distinct vision_ (Ray 2000, 52), is approximately 25 cm. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.
Viewing conditions. If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate. A comfortable viewing distance is also one at which the angle of view is approximately 60° (Ray 2000, 52); at a distance of 25 cm, this corresponds to about 30 cm, approximately the diagonal of an 8″×10″ image. It often may be reasonable to assume that, for whole-image viewing, a final image larger than 8″×10″ will be viewed at a distance correspondingly greater than 25 cm, and for which a larger CoC may be acceptable; the original-image CoC is then the same as that determined from the standard final-image size and viewing distance. But if the larger final image will be viewed at the normal distance of 25 cm, a smaller original-image CoC will be needed to provide acceptable sharpness.
*Enlargement from the original image to the final image. If there is no enlargement (e.g., a contact print of an 8×10 original image), the CoC for the original image is the same as that in the final image. But if, for example, the long dimension of a 35 mm original image is enlarged to 25 cm (10 inches), the enlargement is approximately 7×, and the CoC for the original image is 0.2 mm / 7, or 0.029 mm."*








The resolution of the recording medium could become a factor if it were to drop too low. As such it would be entirely unsuitable for photographic use.

Otherwise the size of the CoC is predicated on human visual acuity and the size of the recording medium (see chart above).

Joe


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## Bebulamar (Mar 22, 2016)

DarkShadow said:


> All this technical crap gives me a migraine.I like to spend less time  thinking about full frame vs crop or FX vs DX glass and spend more time thinking about shooting and Improving. I am happy as a clam with my D7200 and slow sigma 150-600mm and my slow 18-140 kit lens for general walk around things.



Sure the technical isn't necessary! However, it's interesting to some and it's enlightening to think about it.


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## bribrius (Mar 22, 2016)

does anybody actually do photography and make money on it anymore? Seems everyone sells photography gear and talks about it for money instead.


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## Solarflare (Mar 25, 2016)

Thats hard to answer without going offtopic.

I would state that impressing people with photographs is actually very hard.

People as in people who dont know you, only know your photographs. Getting a praise out of people who know you, on the other hand, is almost shockingly trivial.

So a part of this is simply: reviewing gear is simply much easier than making good photographs. Good as in "stands out from the crowd".


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## runnah (Mar 25, 2016)

bribrius said:


> does anybody actually do photography and make money on it anymore? Seems everyone sells photography gear and talks about it for money instead.



Its easier to criticize than create.


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## Derrel (Mar 25, 2016)

Selling photo education (books, workshops, lessons, training programs) has become a major income source for many people in the photo world. Even people who spread utter B.S. can try their hand at educating. The whole idea Tony is spreading, about f/stops being related to the area of the sensor size--that is a BRAND-NEW, 2015-internet-era line of B.S. that was first seen on dPreview, by one of their multiple, new, junior-level writers.


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## Overread (Mar 25, 2016)

I suppose next it will be AF speed or something that drops by crop factor as well! I mean if the sensor is smaller that means less light and that means the AF won't work as well; by the same factor as the crop factor


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## robbins.photo (Mar 25, 2016)

Overread said:


> I suppose next it will be AF speed or something that drops by crop factor as well! I mean if the sensor is smaller that means less light and that means the AF won't work as well; by the same factor as the crop factor



So if I add in a TC on my crop sensor camera I'd better be willing to wait an hour between frames?   Good to know.. quick, somebody shoot a video and put it up on youtube.. lol


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## Derrel (Mar 25, 2016)

Ysarex said:
			
		

> The people making this argument are trying to use "total light gathered" and crop factors as another format "equivalence" function and in this case pertaining to noise. They're claiming that noise comparisons APS versus FF can be made equivalent by applying the crop factor to total light gathered which can then be expressed hand in hand with the DOF equivalence by focusing on the lens f/stop. In other words the APS image (correct exposure at f/2.8) is noisier than the FF image by the amount you would see if you under-exposed the FF sensor to the same scene at f/4.2 when correct exposure was f/2.8. And, Oh great wonder, the DOF would be the same as well. "I'm so damn clever I'm going to make a Youtube!"
> 
> It is true that smaller sensors are inherently noisier than larger sensors: (Clarkvision: Does Pixel Size Matter) because the smaller photosites (pixels) on the smaller sensors gather less light, *but this equivalence rubbish expressed as an f/stop variance in the lens is bleepin' nonsense.* It's far too complex for the likes of Tony's feeble mind to keep straight and express coherently.
> 
> ...



Some of the video low-lights:

1:33  and by 1:45 be prepared for the first dose of fertilizer. "So, you don't get either the, the depth of field, the total light gathered, or the same angle of view, you have to change all of those things.It becomes a very different lens. And I'd like to make the point the focal length probably isn't as useful. I love using 24mm at the wide end..."blah, blah,blah.

6:17 :   "Because it's designed for full frame..and you're just losing all that light that's actually coming in, you're not getting the most out of the lens."

6:30 :  Comparing the Nikon 24-70 f/2.8 on a D6100 and the D3300 with a Sigma 18-35mm f/1.8: "They both gather about the same total light, so in a given environment you could expect them to have about the same amount of noise." blah...blah,blah...


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## Tim Tucker (Mar 25, 2016)

This is the depth of field you should really worry about:


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## table1349 (Mar 28, 2016)

Give one of these to your lense 30 minutes before shooting and all "softness" will go away.   And remember if your lens experiences sharpness for more than four hours you should seek medical relief.


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