# Manual Focus Distance Window On Lens



## decado (Mar 24, 2010)

So on higher end lenses (like my 10-22mm canon) there's a window that shows focus distance to help with manual focus. But I've noticed that all the way at infinity on this is a little out of focus, and I find it hard to focus perfectly by eye. So where exactly on this little scale would be a perfect infinity focus?


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## Overread (Mar 24, 2010)

Most lenses have a little play at the infinty point on the scale, this is to account for small changes in the lens due to things like temperature change (expansion and contraction of materials) and other factors. Often a tiny bit back from it will be infinity but its really something you have to play around with and see.


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## decado (Mar 24, 2010)

Well that's too bad, I'm really bad at getting focus just right. Is it better then to just autofocus a third of the way into the scene for narrow aperture shots instead of trying to manual focus the lens at infinity?


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## Overread (Mar 24, 2010)

Is this for handheld or tripod based shots? If its tripod based you could use an angle finder - even the 3rd party ones (eg Hoodman or Seagull) work well and give a 2* magnification view to the image - that is if you don't have liveview on your camera which also (in most models) has image magnification.

Failing that have you double checked that your diopter in the viewfinder is correctly set?


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## decado (Mar 24, 2010)

It's tripod, I'll try the magnification thing but it's even harder to see on the screen than in the bright viewfinder, maybe I'll try the angle finder. The diopter is correctly set.


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## Joves (Mar 24, 2010)

Well for manual focusing I suggest you get a Split-Prism or, Micro-Prisim screen. Katzeye is one the the places to get one. KatzEye Optics - Custom Focusing Screens


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## white (Mar 24, 2010)

decado said:


> Well that's too bad, I'm really bad at getting focus just right. Is it better then to just autofocus a third of the way into the scene for narrow aperture shots instead of trying to manual focus the lens at infinity?



If your lens has a depth of field scale on the barrel, you could place one end of the aperture bracket at infinity, instead of actually placing the focus marker there. You'll get more depth of field. For example, at f/16 you might get a range of sharpness from 10 ft. to infinity, as opposed to 15 or 20 ft.


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## decado (Mar 25, 2010)

white said:


> decado said:
> 
> 
> > Well that's too bad, I'm really bad at getting focus just right. Is it better then to just autofocus a third of the way into the scene for narrow aperture shots instead of trying to manual focus the lens at infinity?
> ...


I'm not really sure what you mean here.


Joves said:


> Well for manual focusing I suggest you get a  Split-Prism or, Micro-Prisim screen. Katzeye is one the the places to  get one. KatzEye  Optics - Custom Focusing Screens


What exactly are these things?


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## benhasajeep (Mar 25, 2010)

What some are suggesting to you is called hyperfocal focusing.  This is a technique that can be used to increase the dof of a scene.  Newer lenses this is harder to do since lens manufacturers have removed the scales from the lenses for some reason.  But if its a technique you use often you can make your own scales with some tape and a little leg work.

I could write forever trying to describe what I am talking about.  So I will just say look up hyperfocal focusing.  Many many sites on the net gives great information on how and why to use it.

As for your situation I have the same issue with my mf 300 f/2.8 lens.  It is actually at infinity when the focus line is in the middle of the left circle of the infinity symbol.  All I did was put a piece of tape on my lens and mark new lines.  I prefocus the lens all the time for hyperfocal focusing.  So what I have done is a series of tests at each f-stop to find focus for the infinity symbol.  On the piece of tape I made new reference lines for each f stop.  So now I can just prefocus the lens and leave it alone.  No focusing required since most of the time what ever I am taking a picture of is always a bit away from me.


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## Garbz (Mar 25, 2010)

Newer lenses which focus past infinity typically do so due to variances with the zoom scale along with other reasons posted above. I know with one of my lenses (can't remember which off hand now but I think the Nikkor 18-70mm f/3.5-4.5) at 70mm the zoom is much closer to the end of the scale when focusing on a distant object than at 18mm. Likewise if you focus zoom then click rather than zoom focus and click I would end up with a blurry pictures.

On the flip side a misalignment issue in my 105mm macro has caused me to lose infinity focus. Doesn't worry me since I never use infinity on that lens, but this would be heartbreaking if it happened on my wide angle.


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## Joves (Mar 26, 2010)

decado said:


> Joves said:
> 
> 
> > Well for manual focusing I suggest you get a Split-Prism or, Micro-Prisim screen. Katzeye is one the the places to get one. KatzEye Optics - Custom Focusing Screens
> ...


 
It is a good old fashioned focusing screen. Like you had in your old film Slrs. As you focus the center area becomes sharp when you are where you need to be, in the case of the Micro-prism. For the Split the two halves in the center line up.


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## Vautrin (Mar 29, 2010)

The important thing to note here is modern DSLRs are not really designed for manual focusing.  They can support manual focusing more as an afterthought then an actual design decision.

Back in the days of film focusing was hard.  So there were all sorts of aids to be able to focus correctly.

Just go to the used dept of your local camera store (if they still have film cameras) and you'll see what I mean.  Waist level finders with magnifying glasses to make sure things are in focus, focusing screens you can look through that tell you when an item is in focus (that's the katzeyeoptics page someone posted)

But digital cameras don't have any of that because your digital camera is probably better at focusing in the majority of situations then you are.  With top of the line cameras you can maintain focus on a fast moving object in the dark.  And with facial recognition and all sorts of other technologies there's no reason for manufacturers to build in good manual focus.

That's why if you take a lot of new DSLRs on manual focus mode, the pictures might look terrible.  You'll have difficulty seeing if a shot is sharp on the viewfinder -- and a little bit of blurriness will ruin the shot on screen...

I think part of this is due to the fact that smaller digital sensor size yields more depth of field.  So when you look through the view finder with the iris of the lens wide open, you get more depth of field then with a film camera.

I think the best thing is to understand your medium.  Digital camera?  Stick with autofocus except for unusual situations.  Film camera?  Play around with focus all you want..

And don't knock film cameras -- they can be a lot of fun.  With my mamiya (medium format, with something called a waistlevel viewfinder) there's a magnifier built into the viewfinder.  You can see every little bit of the picture -- which parts are out of focus, which are in, and you can see every little detail.


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## decado (Apr 20, 2010)

Vautrin said:


> The important thing to note here is modern DSLRs are not really designed for manual focusing.  They can support manual focusing more as an afterthought then an actual design decision.
> 
> Back in the days of film focusing was hard.  So there were all sorts of aids to be able to focus correctly.
> 
> ...


So then autofocus a third of the way into the scene then for infinity shots?


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## davebmck (Apr 21, 2010)

That's a general rule of thumb, but as posted above the best option is to focus at the hyperfocal distance.  This provides the most DOF with infinity in focus.  Your depth of field will be from half the hyperfocal distance to infinity.  For instance, if you focus at a hyperfocal distance of 10 ft, your DOF will be from 5 ft to infinity.  The hyperfocal distance is a function of aperature and focal length, so you need a table or calculator to determine it for a given set of conditions.  You can find these calculators by searching on the internet.  Some of the smart phones also have apps that calculate the hyperfocal distance and other useful information.


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## decado (Apr 22, 2010)

So how would hyperfocal focusing work with a crop sensor? Do I have to convert the focal length first? If so how does one go about converting that?

Also, an annoying part about hyperfocal focusing on my lens is that when you turn the focusing ring the distance scale (inside a closed window) is what moves while the line stays stationary, add to that the fact that the focusing ring can still be turned when one end of the scale is reached (I could try not to but it's hard for tiny distances not to pass). Add to all that the fact that there aren't lines for the distance numbers inside the window so I have no idea if for example at 1.5ft if the line should be lined up with the 1, before the 1, with the decimal point, or what. Do you see my point? I guess hyperfocal focusing probably isn't going to happen with this lens... Unless are these focusing screens meant for hyperfocal focusing?


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## Garbz (Apr 22, 2010)

How would it work? You go to Understanding the Hyperfocal Distance, fill out the details in the chart below. Hit calculate, and hit print


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## Vautrin (Apr 22, 2010)

A focusing screen just lets you see what's in focus easier, or provides gridlines or other useful tools for composition.

It's just a piece of glass you put between the part you put your eye and the mirror / prism -- it'd either be #5 or #6 in the diagram below:

http://images2.wikia.nocookie.net/__cb20060224221425/photography/images/8/80/Slr-cross-section.png


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## decado (Apr 22, 2010)

Garbz said:


> How would it work? You go to Understanding the Hyperfocal Distance, fill out the details in the chart below. Hit calculate, and hit print



 Two things: First which of those would a 500D be considered? Second, I'm not gonna have that calculator (just a simple hyperfocal calculator) when I'm out and about with my Iphone so what would the calculation be for the crop sensor so I can figure it out?


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## Garbz (Apr 25, 2010)

The 500D is a DSLR with a 1.6x crop factor.

The calculator gives you a table of f stops and focal lengths to give you the hyperfocal distance on each lens. You shouldn't have to re-calculate unless you're changing the definition of sharpness or the film spec (35mm, medium format, etc.). 

So hit calculate, and then hit print


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## davebmck (Apr 25, 2010)

The hyperfocal distance doesn't have anything to do with the crop ratio of the camera.  It is based on the actual focal length and aperture of the lens.  If you have an Iphone, there are a few apps that will calculate the hyperfocal distance for you.


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## Dao (Apr 26, 2010)

davebmck said:


> The hyperfocal distance doesn't have anything to do with the crop ratio of the camera.  It is based on the actual focal length and aperture of the lens.  If you have an Iphone, there are a few apps that will calculate the hyperfocal distance for you.




It does. Hyperfocal distance is related to Depth of Field (Dof).  Dof is related to Circle of confusion (CoC) and CoC is related to medium size.  So Hyperfocal distance varies with sensor size.

OP, besides using hyperfocal distance, since you have a T1i/500D, I believe the camera has liveview.  And you can also use that to nail your focus (esp on a tripod).


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## davebmck (Apr 26, 2010)

I stand corrected.  The hyperfocal distance is based on the effective focal length, not the actual focal length.


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## Garbz (Apr 27, 2010)

davebmck said:


> I stand corrected.  The hyperfocal distance is based on the effective focal length, not the actual focal length.



The hyperfocal distance is based on a definition of acceptably sharp, no more, no less. Variables that feed into that are focal length, aperture, and effective sharpness at a given distance. Effective sharpness encapsulates crop factor, print size, print viewing distance and the eye-sight of the viewer.


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## Dao (Apr 27, 2010)

Garbz said:


> Effective sharpness encapsulates crop factor, print size, print viewing distance and the eye-sight of the viewer.




:thumbup::thumbup:

And that is how the CoC is defined.

I do not know the exact details, but I think in 35mm world, the CoC was calculated with regular 35mm film size, printed on a regular photo size (i.e. 4x6) and view it at regular distance (such as arm length).


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## Vautrin (Apr 27, 2010)

So can I just ask a stupid question?

If I focus my lens to infinity, and take a photo at f 2.8 and a photo at f 22, will they have the same depth of field, or a different depth of field?


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## Aye-non Oh-non Imus (Apr 27, 2010)

This was an interesting video from Bryan Peterson for story telling photos with wide angle lenses.

You can see it [ame="http://www.youtube.com/watch?v=uQ6DqhPuPpQ"]*here*[/ame].[ame="http://www.youtube.com/watch?v=uQ6DqhPuPpQ"][/ame]


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## Vautrin (Apr 27, 2010)

Well maybe I should rephrase.

Before Garbz post I had thought hyperfocal distance is a way to get as much in the scene as possible sharp.  So you focus to 1m, and you know everything from 0.5m to infinity will be sharp at f22 

Maybe I'm misreading the post but Garbz you seem to suggest that everything might not be tack sharp at f22?  So if I focus to infinity and f22 will I have more tack sharp depth of field then at f2.8 focused on infinity?

Of when you focus on infinity do you give up the focus before infinity on your lens?


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## Dao (Apr 27, 2010)

You may want to play around with the DoF calculator.

Online Depth of Field Calculator


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## davebmck (Apr 27, 2010)

What Garbz is saying is that the part of the image that is within the DOF is acceptably sharp.  Not everything will be tack sharp.  At some distance, the image will be the sharpest and the rest will fall into the acceptable range as defined by the circle of confusion.

To answer your question, the image taken at f22 will have a greater DOF than the image taken at f2.8.


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## Overread (Apr 27, 2010)

However you might want to use f8 - f16 with f10 - f13 being the more common apertures used; rather than using apertures smaller than f16. This is because diffraction starts to take place within most lens and camera setups around the f10 point - by f13 its normally still a very usable image - f16 tends to waver either way and going any smaller and diffraction starts to take over. 

What is the effect of diffraction? Its simply softness in your image - no matter how well you shoot the softness will be present because its a part of the properties of lens+camera operation. Thus that is why we don't simply stop all the way down to take landscape shots and instead use wider apertures along with hyperfocal focusing to get landscape shots that are acceptably sharp.


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## table1349 (Apr 27, 2010)

In practical terms the difference in the circle of confusion between a FF Canon at 0.030mm and a 1.6 crop sensor camera at 0.19mm is slight.  Do the math.

Hyperfocal distance, near distance of acceptable sharpness, and far  distance of acceptable sharpness are calculated using the following  equations* (from Greenleaf, Allen R., Photographic Optics, The  MacMillan Company, New York, 1950, pp. 25-27)*:

Hyperfocal distance:





  Near distance of acceptable sharpness:




  Far distance of acceptable sharpness:




   where:

_H_
is the  hyperfocal distance, mm
_f_
is the lens focal  length, mm
_s_
is the focus distance
_Dn_
is the near  distance for acceptable sharpness
_Df_
is the far  distance for acceptable sharpness
_N_
is the f-number
_c_
is the circle of  confusion, mm

f-number is calculated by the definition _N = 2i/2 ,  _where _i = 1, 2, 3,..._ for _f/1.4, f/2, f/2.8,..._


Calculations using these equations must use consistent units.  When  focal length and circle of confusion have units of millimeters, the  calculated hyperfocal distance will have units of millimeters.  To  convert to feet, divide _H_ by 304.8. To convert to meters, divide _H_  by 1000.


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## Garbz (Apr 28, 2010)

Well there you have it. Take graphics calculators with you folks 



Vautrin said:


> Maybe I'm misreading the post but Garbz you seem to suggest that everything might not be tack sharp at f22?  So if I focus to infinity and f22 will I have more tack sharp depth of field then at f2.8 focused on infinity?
> 
> Of when you focus on infinity do you give up the focus before infinity on your lens?


The easiest way to visualise this would be a series of bell curves. Which look like this: http://willohroots.files.wordpress.com/2009/09/bell_curve.jpg incase you don't know what I'm talking about. 

With the horizontal axis being the distance, the middle of the bell curve the focus point, and the vertical axis sharpness. Now imagine at f/2.8 that bell curve is very very thin. Sharpness drops off quickly from the focal point. At f/22 the bell curve is very very fat. Sharpness will drop off slowly, but it it will drop off, i.e. It WILL have a peak sharpness as before.

The hyperfocal distance defines an "acceptable" sharpness whereby a normal person with normal vision using a 35mm film camera looking at a 6x4 print from a normal distance of arms length (correct me, i'm not sure on this) can not notice a visible difference between the focus point and the infinity point.

This all gets tossed out the window if you decide to print say a 40" wide print. The person now probably standing pretty close will see much more detail (meaning the circle of confusion is smaller). Thus even if it's the same image as the 6x4 they will now see that the background may not be quite as sharp as the focal point.

A work around for this is to find the hyperfocal distance and then focus a bit behind it. By pushing the focus point back you're moving your bell curve closer to to the back meaning that sudden cut-off at infinity would be at a higher point on the curve (sharper).  But one thing you can not do is take a picture, and then zoom in as far as possible on the digital camera. Again the CoF would be different than when viewing the print, or when viewing it on your monitor. 

*Summary*: You're right, I'm suggesting everything may not be tac sharp at f/22. There will still be one single point of ultimate sharpness. Everything else will just appear sharper than at f/2.8


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## Vautrin (Apr 28, 2010)

So let's say I stop down to f 32.  Yes, there's diffraction so the center of the bell curve will be less peaked, but will the tails be fatter and longer?


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## Overread (Apr 28, 2010)

Essentially yes they will be however the following two images might give you an idea of diffraction

f5point6 at 5 times on Flickr - Photo Sharing!

f16 at 5 times on Flickr - Photo Sharing!

The aperture values on the listed shots are a little obscure because of the nature of the lens in question, but it gives a good showing of the sort of thing you are expecting to see. The "f16" shot has a very high depth whilst the f5.6 lacks this - however you can clearly see that the f16 shot is soft all over dispite being taken exactly the same way as the far sharper f5.6 shot.

Sadly this is macro so the 5.6 does not show the hyperfocal distance aspect, but as an (extreme) diffraction display it works rather well.


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## Vautrin (Apr 28, 2010)

Very useful...Thank you...


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