focusing screen and auto focus

Can a focusing screen mess with the AF? it seems like i have such a hard time nailing focus with the outer points on my 5d2 lately. it seems ever since i put in the new focusing screen, my images have been soft.

Soft? Not sharp anywhere? The focusing screen isn't part of the AF system at all, but if you didn't get it perfectly aligned the indicated AF points might not match the actual AF points (which are behind the reflex mirror and at the bottom of the mirror box) and that would throw your efforts off.

im pretty sure its on properly. must be my technique then.

I seem to remember that with some focussing screens you need to change a custom function on the camera to say you are using that type (for the one series anyway, don't know about the 5's).

Check your custom functions/manual and see, I think it was to do with exposure not focussing but may be worth checking.

All the best

BearSummer

BearSummer wrote in post #17861062
I seem to remember that with some focussing screens you need to change a custom function on the camera to say you are using that type (for the one series anyway, don't know about the 5's).

Check your custom functions/manual and see, I think it was to do with exposure not focussing but may be worth checking.

All the best

BearSummer

That setting is for the metering system, not the AF. The metering sensor is after the focus screen in the optical path, so the light transmission level of the focus screen will affect the amount of light reaching the metering sensor. So if the meter is to retain it's calibration you have to let the camera know which of the screens is fitted to the camera.

Alan

I needed to set a function previously. The metering was off. That hasn't been an issue. I was just wondering about the af but I guess I'm still figuring out the 135L needs really fast shutters as I get older.

Set up on a tripod, using mirror lock-up and using a cable release or the self-timer to trip the shutter and see if you get "soft" images or not. That'll eliminate you as a factor in assessing the situation. If it's still soft overall, try the same set-up and focusing with Live View and see what you get. If it's still soft overall, it may be time to get the lens looked at (try it on another camera too, just in case). If using a tripod with LV gives better results than without, you may need to use focus adjust. If just a tripod an mirror lockup give you good results, it's time to experiment with how fast a shutter speed you need for consistent sharp images - start at 1/4000 and work down. The rule of thumb is 1/f.l. for full-frame bodies, so at least 1/125 on the 135; 1/180 would be better. Even there, pixel-peeping typically will show some degree of blurring.

i've owned this lens for a while, its very sharp and hasn't been banged around so i doubt its just went bad... I wanted to start playing with manual focus, hence the focus screen.

I took the kids out yesterday to fool around with a portable strobe, so i set my shutter at 1/160 in which almost every image was blurry or soft. when i put the strobe away the faster shutter shots were better although the shutters were around 1/400, 1/500, 1/640 they seemed sharp (ie no motion blur), but it seems focus was missed (i was using outer points).

I just dont remember this lens giving me such problems as it has since the focusing screen was installed a few months ago.

Maybe i need to do some micro adjust on it.

Yes, you do need to go into the menu and tell the camera which focusing screen it's installed.

mike_311 wrote in post #17861560
i've owned this lens for a while, its very sharp and hasn't been banged around so i doubt its just went bad... I wanted to start playing with manual focus, hence the focus screen.

I took the kids out yesterday to fool around with a portable strobe, so i set my shutter at 1/160 in which almost every image was blurry or soft. when i put the strobe away the faster shutter shots were better although the shutters were around 1/400, 1/500, 1/640 they seemed sharp (ie no motion blur), but it seems focus was missed (i was using outer points).

I just dont remember this lens giving me such problems as it has since the focusing screen was installed a few months ago.

Maybe i need to do some micro adjust on it.

I may have misunderstood - are you using AF or MF?

If MF, are you assessing focus through the viewfinder (I assume so, otherwise there is no need for a focussing screen)? Have you checked your dioptre setting? Do you need glasses for short focal distances? Or, vice versa, use glasses but the prescription is wrong at short focus distances? Just some thoughts.

If AF, then I find that my OOF shots with the 135L are usually due to the narrow DOF (after ruling out motion blur). I can't blame the lens for that . . .

AF and yes the issue are with narrow DOF, it seems the focus is off. if At f2 if i shoot a headshot and put the af point on an eye, i expect the eye to be sharp. its not. it used to be.

part of my problem is slow shutters and subject blur/camera shake. but at higher shutters i expect sharpness. I thought maybe the focusing screen could be affecting it since that seems to be when the issues started.

yesterday i performed a MA and the lens was backfocusing a little. I adjusted it and did a quick shoot yesterday with some really shallow DOF compositions. I haven't had a chance to look at them yet to see if its better.

micros adjust seems to have worked, however the two extreme points are slightly off. i guess i just wont use them.