True wide open D of F on focusing screen

[keith_lubow]

Hello,

 

Is there a screen available for modern cameras that shows accurate D of F with

fast lenses? Wide open I get the D of F of about f/2.8. Anything shot at a

larger aperture has less D of F than I see. I heard the exact reason for this at

one time, but have forgotten.

 

Thanks,

 

Keith

[ken schwarz]

Depends on the camera. Those with interchangeable screens will accept a ground-glass focusing screen that helps you discriminate finer focus than the standard bright screens of modern AF cameras.

[sheldonnalos]

The Canon Ee-S screen (for the 5D) is optimized to snap in/out of focus more clearly when used with fast aperture lenses, at the tradeoff of a darker viewfinder.

 

The real reason for the apparent greater DOF in the viewfinder is because it's small. As you increase print/image size, the amount of DOF decreases. An 8x10 or 11x14 print will show the plane of focus much more clearly (less apparent DOF) than you can see in the camera viewfinder.

[andre_stull]

Had the same problem with my 50 1.4 on 5D. Bought the ee-s screen for D of F and manual focusing in low light. Works perfectly. 40D uses the ef-s screen for this ability. All 1D series cameras have interchangeable screens.

 

They cost around 35 bucks. Easy to change with Canon kit that comes with screens. Called Super Precision Matte screens. Auto focus accuracy improves as well. Great upgrade. Viewfinder will be a little darker with lenses slower than 2.8 but not bad enough to switch screens constantly.

 

Best upgrade I have done for only 35 bucks! And much higher keeper rate.

[istvan_sandor]

"Auto focus accuracy improves as well"

 

Andre, autofocus has nothing to do with the focusing screens.

The AF sensors are located in the lower part of the mirror chamber and receive the light with the mean of the so called sub mirrors which are located under the main mirror.

The light that comes in through the lens goes into two different directions: one part of it goes towards the viewfinder (i.e. the focusing screen)with the help of the main mirror and the other part is directed to the AF sensors by the sub mirror.

Therefore, AF is completely independent from what focusing screen one is using.

Agree however, that the EF-S is great for MF with fast lenses !

Istvan

[keith_lubow]

The cameras in question are a 1D Mk. I, 1Ds Mk. I, 1D Mk. II N, 10D, 20D, and EOS 1 film bodies. I know several screens are made for the pro bodies, and there are even some aftermarket ones that can be installed into the 1.6 bodies. Just not sure which (if any) will give me true D of F at 1.2 through 2.8.

 

Thanks for the replies thus far.

 

Keith

[brucecyr]

I may have lived a sheltered photographic life, but I've never heard of a focusing screen that does DOF! I thought that was what the DOF button was for.

[keith_lubow]

Modern focusing screens do not show proper d of f in the viewfinder on a lens faster than f/2.8. Pretty flipping idiotic if you ask me.

 

Keith

[brucecyr]

OK, I'm probably flipping idiotic too, because I don't understand. Are you suggesting a visual representation of DOF, say maybe slight darkening of areas out of the DOF at a given aperture? That would be neat if it could be done! They could even allow the user to tune the definition of DOF by specifying a CoC in the custom functions!

[keith_lubow]

Upon normal viewing, an auto-aperture lens is wide open. However, with modern focusing screens, all you see is the D of F of f/2.8. I have tested this by shooting text on a page. In the viewfinder I might have seen three or four letters in focus. On the LCD, perhaps one and a half at f/1.2.

 

This leads to missed focus extremely often in low light, in which I have been trying to use this lens. The focus confirmation dot helps a little, but not much.

 

Keith

[brucecyr]

Finally I think I'm reading a clear statement of what the problem is!

 

But I'm skeptical. You're saying that the viewscreen affects DOF to raise it when the lens is open more than f2.8! But what happens when you shoot at a narrower aperture and physically stop down to see DOF? Does the screen stop working? Or does it also affect DOF under those circumstances? If so, how?

 

I have trouble trying to duplicate your steps because the fastest lens I have is f1.7, and that is a manual focus one. Also I don't have any of the exalted cameras you're lucky enough to own -- all I got a rinky dink 350D with a Katzeye OptiBright screen.

 

In this case at least, I'm semi-confident that the screen's apparent DOF is at least monotonically related to the lens' aperture settings, that is, I see the least DOF at f1.7, maybe I see more at f2.0, definitely I see more at f2.8.

 

Until someone convinces me otherwise, I don't believe that there is a technology that allows viewing screens to increase the apparent DOF delivered below f2.8 by a lens' actual aperture.

[brucecyr]

PS: Minor point, but I'm not sure the stop between indicated 1.7 and 2.8 is 2.0 or 1.8. If the latter, no wonder I couldn't see a difference from 1.7!

[keith_lubow]

Everything works as you think it would with D of F preview once you stop down past f/2.8. But stop up to larger aperture than f/2.8, and D of F preview shows the same D of F as at f/2.8. It has something to do with the design of modern screens compared to older ones, or so I have been told.

 

Keith