7D viewfinder DOF doesn't match image DOF?

If I remember my OM1n used to have a fresnel focussing screen and that was all manual focussing, admitedly it did have a split prism in the centre to assist things.

You're experiencing part of the reason I wasn't happy that they went with a non-interchangeable focus screen on the 7D, although some third-party companies have come out with aftermarket focusing screens for the camera.

I changed the FS on my 5D for the Ee-S (super precision) FS, and it makes manual focusing and judgment of DoF a lot easier, but yes, it's darker.

It's not just the focusing screen. The viewfinder also has an eyepiece. The eyepiece has a magnification value. The optics in the eyepiece affect the depth of field. The only way to really see the true depth of field is with a view camera which has a ground glass back which you replace with the film back when you're ready to shoot. Otherwise the optics in the middle change it quite a bit.

The biggest viewfinders generally have less magnification and hence are closer to the true depth of field. The Rebel's tiny VF is the worst but even the 5D and 1D's viewfinder are not true to the depth of field. High magnification, a smaller image also makes it brighter which most people like. Since most people use zooms, especially slow consumer zooms on the Rebel, the tiny VF is usually OK.

If you have time to worry about the precise DOF, throw it in Live View.

While focusing screens may make it easier to see fine focus differences and easier to judge where "in the VF field of view" the OOF transition begins, DoF is TOTALLY dependent on the size of the image you look at. The DoF you see on the focusing screen is NOT what you will see on a 8x12 print and what you see on an 8x12 print will be different from what you see on a 16x24 print. The enlargement factor is an intrinsic component of affecting what seems to be in focus and that's what determines DoF.

Poe wrote in post #9834875
Read through it once. My initial thoughts are, the 7D VF has 100% image coverage, so why does it, based on Ken R., not see the other light rays from the outer edges of the lens but the sensor does? Will read through it some more and try to find other explanations. His leaves me wanting, still.

Youre confusing VF coverage with the type of focusing screen used. Focus screens in modern cameras are made to be brighter which causes them to show more DOF than will actually be recorded. Its not specific to the 7D. Every DSLR will work this way from the factory including my old 20D that I bought 6 years ago (which was when I first noticed it as well).

IIRC, optical tricks are used on the standard viewfinder to enhance brightness. Those optical measures set the effective max aperture to about f2.4, regardless what max aperture the lens has. As stated above, the S-Screens don't use that optical tricks, are thus darker but give a realistic DOF impression when using a lens @ 2.2 or faster.

DoF is not a property of the image alone.

Are you zooming in on the LCD to review focus?

Any time you change the size of the image to look at it the DoF will be different.

1. DOF perception is totally dependent upon the eye's ability to perceive the out-of-focus blur circles (Circle of Confusion) that represent points that are out of focus. The assumption is that the image for the DOF table/chart is an 8"x10" print which is viewed at a distance of 10". Your viewfinder is much smaller than an 8x10", so DOF perception is impaired simply by size of image being assessed! It is analogous to viewing a 4x6 print to represent the DOF seen in the 8x12" print...it is NOT the same!

2. Coarseness of the focusing screen definitely has a direct relationship on DOF perception. And dSLRs do have less coarseness than older SLRs because the reflex mirror is half sivered to deflect light down to the AF sensor, so they make up for the reduced viewfinder brightness by using a brighter, less coarse focusing screen, which masks DOF perception.

Poe wrote in post #9833772
I just got my 50 1.4 and my 85 1.8 and have been testing the 85 especially, on the 7D. I've noticed that the viewfinder seems to show a larger(deeper) DOF than what actually shows up(shallower) in the image when I review it on the LCD screen. Has anyone else noticed this phenomenon?

What you are seeing is a major flaw in the EOS 7D that hardly anybody ever talks about. The new focusing screen with in-demand grids and AF layouts has one huge drawback: it's incapable of representing accurate depth of field for apertures larger than f/4.0. So if you're trying to manually focus an f1.4 lens through the viewfinder of a 7D, then you're out of luck. The viewfinder is showing you 3 stops greater depth of field than there really is. Needless to say, that is a huge margin for error.

That is the reason why Canon opted not to implement the 7D's high tech focusing screen on the EOS 1D Mark IV. They didn't want their flagship camera to be hampered by an imprecise viewfinder.

All other EOS digital SLRs have default focusing screens that are capable of rendering accurate depth of field up to f/2.8. Most of them can be outfitted with interchangeable focusing screens, which enhances the precision even more. The EOS 7D's flaw is exacerbated by the fact that the camera doesn't even allow for interchangeable focusing screens.

Live View is the only way to do manual focus realiably on a 7D:

http://digitaljournali​st.org/issue0910/tech-tips.html

stargazer78 wrote in post #9842230
Live View is the only way to do manual focus realiably on a 7D:

Live View on the 7D is like having a super-ground glass back. You can see exposure, DOF, 5 and 10x zoom, as well as histogram and grid lines.

I use the DOF button to toggle between Servo and One Shot, anyway.

TJH

I've not noticed it myself, but one thing I would mention is that knowing how the human eye works, it will focus on a single point rather than seeing the overall picture, and this may create the impression of a deeper depth of field than is represented in image.
Don't know if this is the root of the problem. But worth bearing in mind.

stargazer78 wrote in post #9842230
What you are seeing is a major flaw in the EOS 7D that hardly anybody ever talks about. The new focusing screen with in-demand grids and AF layouts has one huge drawback: it's incapable of representing accurate depth of field for apertures larger than f/4.0. So if you're trying to manually focus an f1.4 lens through the viewfinder of a 7D, then you're out of luck. The viewfinder is showing you 3 stops greater depth of field than there really is. Needless to say, that is a huge margin for error.

That is the reason why Canon opted not to implement the 7D's high tech focusing screen on the EOS 1D Mark IV. They didn't want their flagship camera to be hampered by an imprecise viewfinder.

All other EOS digital SLRs have default focusing screens that are capable of rendering accurate depth of field up to f/2.8. Most of them can be outfitted with interchangeable focusing screens, which enhances the precision even more. The EOS 7D's flaw is exacerbated by the fact that the camera doesn't even allow for interchangeable focusing screens.

Live View is the only way to do manual focus realiably on a 7D:

http://digitaljournali​st.org/issue0910/tech-tips.html

Thanks stargazer. Didn't know it was in an issue of tech-tips. I think this answers my question.

stargazer78 wrote in post #9842230
What you are seeing is a major flaw in the EOS 7D that hardly anybody ever talks about. The new focusing screen with in-demand grids and AF layouts has one huge drawback: it's incapable of representing accurate depth of field for apertures larger than f/4.0. So if you're trying to manually focus an f1.4 lens through the viewfinder of a 7D, then you're out of luck. The viewfinder is showing you 3 stops greater depth of field than there really is. Needless to say, that is a huge margin for error.

That is the reason why Canon opted not to implement the 7D's high tech focusing screen on the EOS 1D Mark IV. They didn't want their flagship camera to be hampered by an imprecise viewfinder.

All other EOS digital SLRs have default focusing screens that are capable of rendering accurate depth of field up to f/2.8. Most of them can be outfitted with interchangeable focusing screens, which enhances the precision even more. The EOS 7D's flaw is exacerbated by the fact that the camera doesn't even allow for interchangeable focusing screens.

Live View is the only way to do manual focus realiably on a 7D:

http://digitaljournali​st.org/issue0910/tech-tips.html

+1!

Hi All.

This thread has been very helpful to me, especially the link to Chuck's comments. Thanks Stargazer!

Does anyone have any success stories of using screens from focusingscreen.com?

The ability to use such screens, especially the S-type, is a major consideration in my deciding whether to buy or not to buy a 7D.

For the kind of photography that I usually do (subjects that are moving), Live View focusing is not an option. I would appreciate any kind responses.

Thanks!

Regards,
bill

To me, the 7D is a wonderful camera, but its most significant flaw is the relative inability to change focusing screens, so that one can better tailor its viewfinder to one's own preferences. But I am very accustomed to having focusing screen interchangeability in all my SLRs used over the past 35 years!

Live View is not a good option not only for moving subjects, but also for when you want precision focus while not mounted on a tripod or braced against an immoveable object...your body sways back and forth with respiration and heartbeat much more than you realize (folks, rifle marksmen understand that body motion issue and have methods to compensate, and standing while aiming is not the most precise way to aim a rifle!). Macro shooters, who are accustomed to the very shallow DOF, know this body sway issue for trying to do macro work hand held.

And why on earth should we rely upon the very unsteady practice of holding a camera out at arm's length like a snapshooter with P&S (rather than the advantages of the 3-point brace for aiming any SLR), that we chose to get away from?!

As for focusing screen options for non-7D users, one has to realize that without an CFn selection provided by Canon for a non-standard focusing screen, there are metering error problems that are introduced. If you use only Evaluative and all focusing points active (which many amatuers do), you can get away without metering issues mostly. But if you use Center focus only, and/or you use Spot metering, lenses slower than f/4 are increasingly in error for metering (some have experienced 2-3EV of error!) with the non-Canon focusing screens which are on the aftermarket.

But, given the inherent reasons that DOF preview in any SLR is only a poor approximation of the actual DOF seen in the final print, even a film SLR with a good focusing screen (not optimized for brightess, as AF camera viewfinders are) is not to be relied upon for DOF.