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06-03-2011, 08:59 AM   #1
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view finder DOF

I cannot see the same effect through my viewfinder as I do on my lcd screen or computer screen. If I have a shallow DOF it doesn't seem even close to as shallow as it is when looking through the viewfinder. This is one of the reasons I find it hard to focus when using shallow DOF. Is it just me???

06-03-2011, 09:21 AM   #2
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QuoteOriginally posted by mhaws Quote
I cannot see the same effect through my viewfinder as I do on my lcd screen or computer screen. If I have a shallow DOF it doesn't seem even close to as shallow as it is when looking through the viewfinder. This is one of the reasons I find it hard to focus when using shallow DOF. Is it just me???
Nope, it's not just you. "Standard" focusing screens are compromises on the DoF front in order to maximize brightness. The ultimate DoF-oriented focusing screen is supposedly the Canon EE-S. There is a recent thread here that discusses modifying these for Pentax use. Katzeye split-screens will also help quite a bit, but apparently not to the extremely shallow DoF's that the EE-S will. I personally use a Katzeye and find that it suits me just fine.

Last edited by DogLover; 06-03-2011 at 09:38 AM.
06-03-2011, 09:22 AM   #3
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No, it's not just you. I find DOF very difficult to see in a half-frame VF. It's much easier with full-frame, which is part of why I still love and use FF film SLR's. You'll get a better DOF preview using LiveView.

Some of my thin-DOF focusing tricks:

* Use Catch-In-Focus. This mostly applies to manual-focus lenses, but can be used with AFL's also.
* Use spot focus and center the subject. Don't worry about what isn't centered. Recompose in PP.
* Use a Katzeye-type split focus screen. But subjects need to be well-lit, with a strong contrast area.
* Refocus and bracket shots, if the subject will hold still long enough. Dead subjects are easier.
* Cheat. Stop-down a bit for thicker DOF, then blur the background in PP. Do whatever it takes.
06-03-2011, 09:25 AM   #4
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That's normal. You are focusing with the lens wide open (aside from loss of light through mirrors and focusing screen etc) and the narrowest depth of field. The lens only stops down when the photo is taken. If it were to stop down beforehand then at higher f-stops (narrow apertures) you wouldn't get enough light through to see much of anything.
You need to understand aperture and DOF and get a feel for what to use. Depth of Field Preview can help.


Last edited by Bill_R; 06-03-2011 at 09:39 AM.
06-03-2011, 09:30 AM   #5
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Nobody can see DOF very well on a small image; even live view images are too small to give more than vague idea of how the image will appear when displayed at full width.
06-03-2011, 10:42 AM   #6
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Ooops! You discovered one of the dirty little secrets of SLR photography and DOF preview in particular!

The DOF as seen in the viewfinder is an approximation of what you may see in the final image. Viewing size and viewing distance is everything in the world of DOF.
A small image will always appear to have greater DOF than a larger version of the same thing.
For example...compare the photo below to my avatar picture. The only difference is size...


K10D, LZOS Jupiter-9 85/2


Now stand on the other side of the room and look at your screen. Amazing isn't it Pixel peep and the DOF becomes razor thin! One commonly-used solution is to magnify the live-view image with a viewing loupe (4x-8x) to allow for more accurate critical focusing. Another is to buy a focus screen with some sort of focus aid. (I bought a Katz Eye for exactly that purpose.)


Steve

Last edited by stevebrot; 06-03-2011 at 10:49 AM.
06-03-2011, 10:46 AM   #7
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Most DSLR focusing screens are made to make slow kit lenses appear as bright as possible: because of this, when you put a faster lens on there, they are gathering more light from straighter on and not prioritising the rest of the lens, .... net effect, you don't see much difference wider open than f 2.4 or 3.5. This is why I keep wishing Pentax (or anyone) would make a 'screen for fast lenses,' as in days of old: ...ie something not made for 3.5 and slower.
06-03-2011, 10:59 AM   #8
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QuoteOriginally posted by Ratmagiclady Quote
Most DSLR focusing screens are made to make slow kit lenses appear as bright as possible: because of this, when you put a faster lens on there, they are gathering more light from straighter on and not prioritising the rest of the lens, .... net effect, you don't see much difference wider open than f 2.4 or 3.5. This is why I keep wishing Pentax (or anyone) would make a 'screen for fast lenses,' as in days of old: ...ie something not made for 3.5 and slower.
As I said above, the Canon EE-S is made exactly for that. Supposedly it can delineate DoF down to f/1.7. Search here for a thread about modifying it for Pentax use.

06-03-2011, 11:07 AM   #9
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It's the focusing screen and design:

QuoteQuote:
Actually it's mostly the "ground" glass, which is not a ground glass anymore: it's a microstructured glass, optimized for light transmission with slow lenses, not for ease of manual focusing.

Ken Rockwell suggests a simple experiment: "Look through the front of your fast lens at the focus screen. It's black outside the area of the lens that corresponds to f/2.5!". Try it! You will clearly see that no light comes through the outer part of the lens. If light cannot travel one way, it cannot travel the other way: only the light rays that hit close to the center of the lens can get through the eyepiece.
Depth-of-field preview, optical viewfinder, Canon 500D, large aperture - Photography - Stack Exchange
06-04-2011, 11:03 AM   #10
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QuoteOriginally posted by Ratmagiclady Quote
Most DSLR focusing screens are made to make slow kit lenses appear as bright as possible: because of this, when you put a faster lens on there, they are gathering more light from straighter on and not prioritising the rest of the lens, .... net effect, you don't see much difference wider open than f 2.4 or 3.5. This is why I keep wishing Pentax (or anyone) would make a 'screen for fast lenses,' as in days of old: ...ie something not made for 3.5 and slower.
Thanks for mentioning this. The stock focus screen show DOF equivalent to a maximum of about f/3.5-f/4 regardless of the actual aperture. I first discovered this when I got my Jupiter-9 and could not figure out why I was constantly missing focus with the stock screen on my K10D. I switched to the Katz Eye and things are much better now, though it is tempting to try one of the much-discussed Canon "S" screens.


Steve
06-04-2011, 06:13 PM   #11
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Is there some place you know of that explains how a KatzEye focusing screen works? I think I'd like to get one if it would help me to focus better. are these hard to put on the camera? I've never heard of it
06-04-2011, 06:43 PM   #12
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QuoteOriginally posted by mhaws Quote
Is there some place you know of that explains how a KatzEye focusing screen works? I think I'd like to get one if it would help me to focus better. are these hard to put on the camera? I've never heard of it
Go here: KatzEye™ Optics - Custom Focusing Screens

They have instructions on how to install or they can do it for you if you send them your camera. Installing is easy, calibrating (done with different thickness shims) can be a little tedious. If they install, they also calibrate and clean your mirror box.
06-09-2011, 07:57 AM   #13
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I sense another myth in the making I wish people would realize that depth of field does not have sharp limits, it is all related to the circle of confusion parameter, which in this case is the 'grain' size of the focusing screen.

Last edited by kh1234567890; 06-10-2011 at 10:17 AM.
06-11-2011, 05:43 PM   #14
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Can you explain a little more? Or provide a link? I have heard of circle of confusion but I thought it was in relation to the finest detail the eye could detect on a print.
06-12-2011, 04:06 AM   #15
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There are really two answers.

Firstly, depth of field does not have sharp limits - it is a distance range in which a point on the subject will appear as a point (or damn near as one) in the image. The 'damn near as one' criterion is related to the 'circle of confusion' parameter.

Then we get onto focusing screens. With a SLR what you see in the viewfinder is an image projected onto the focusing screen. The pentaprism or pentamirror then flip this the right way up and left to right for your convenience.

Light comes through your lens, bounces off the mirror, hits the focusing screen and is scattered by the matte surface. You then look at this surface (from its back side) and see an image, this being effectively bits of the rough matte surface lighting up or staying dark, depending on what you are pointing the camera at.

Obviously this light is scattered in any which direction, so to make the image brighter the top (facing the pentaprism) side of the focusing screen usually has a fresnel lens on it. This directs more of the scattered light in the direction you want, towards your eye, making the viewfinder look brighter.

The engineering compromise is in making the size and sharpness of the profile of the matte microstructure such that it is as fine as possible while being coarse enough to remain bright. You need the fineness so that you can see detail - and judge depth of focus.

The other extreme are the microprism clear field screens which do not have the matte surface and are therefore very bright. But with them you don't get the depth of field illusion.

Check out this thread for more, much of it is applicable to SLRs also.

Last edited by kh1234567890; 06-12-2011 at 04:19 AM.
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