Where is the AF sensor on the 400d(XTi)

Or, would a manual focus screen screw up the AF ability on the camera?

Reason i ask is that either my screen screws up the auto focus, or i need to learn how to use autofocus better. It seems about 90%, or more, of the shots i took on Saturday(about 400) were out of focus. I just recently installed a manual focus screen so i am curious.

Thanks,
-Dusty-

Most likely, you turned it upside down; check that our first.

what do you mean by autofocus on camera? auto focusing as far as i know is at the lens which sets the focus automatically atleast for my xti. but AF thru the body. hmmmm if there is one probably mine's turn on AF always.=)

owwww, i got it now...=) the AF focus point.=) i think the reason why its out of focus is that the ability to judge how to controll your shutter,and the aperture you've set. manual focus gives you more flexibility on how you prefer your shots would look like. i dn't think manual focus screws up anything.

ratindahat wrote in post #4454157
Or, would a manual focus screen screw up the AF ability on the camera?

No, it won't affect AF. Of course, the manual focus screen does not have any of the AF indicators that the factory screen does (AF boxes and reflectors for the red LEDs). It's possible that you have the wrong AF point selected and with the red LEDs not showing you don't notice it.

The AF subsystem is in the bottom of the camera. If you remove the lens and look under the mirrors at the bottom of the mirror chamber, you can see the openings into the AF lens system.

Also, you'll see two mirrors, one behind the main reflex mirror. The reflex mirror is transparent and it passes light to the AF mirror. That mirror reflects the light to the AF system on the bottom of the camera, and the sensors in the bottom detect contrast in the light.

The manual focus screen, as you may well know, is on the top of the mirror box right under the prism. In some Canon cameras (I know the 20D, 30D and 40D, I think the 350D and 400D as well, and I believe all of the 1/5 series) the superimposed AF point selectors and focus screen are separate. If you pull out your focus screen and look up under the screen, you'll see a transparent plate with boxes. If you don't, and the boxes are on your focus screen, then your camera has no superimposement plate. If the focus screen has no markings, the plate is separate. If the plate is gone or in incorrectly, or if your focus screen isn't in correctly, then you might not see the AF boxes flash in the viewfinder. If so, your camera may not be focusing where you want.

That said, try a focus test with a focus chart on all your lenses. Could be miscalibration.

might be a dumb question, butwhere do i find a focus chart?

just search google for "printable focus chart"...

as for AF, it's located below the mirror, but the auto-exposure sensor is located in the viewfinder, so an MF screen may mess it up. if you didn't install the mf screen properly (not even sure you should do it yourself), there's a high chance 100% of your MF'ed shots will fail, though AF should still work fine.

replacing the screen is not very hard. the AF focus is what doesn't seem to be working well. Guess i will check out a focus chart tomorrow and see what happens.

-Dusty-

ratindahat wrote in post #4455551
might be a dumb question, butwhere do i find a focus chart?

Try this one Dusty : http://www.focustestch​art.com/chart.html

If you scroll to the bottom of the article you can see the test chart (which you need to download). Ignore any D70 references.

Just a couple of thoughts/questions?

Before you changed the focus screen did the camera AF (auto focus) correctly & sharp?

Are you using a replacment screen that others have reported as being one that is a 'reliable' after market replacment? I was not aware that Canon have such alternate screens for the XTi

Lastly, and if I understood your OP it is possible that replacing the screen has caused an issue (see my questions above) because on the 40D (1 series as well?) changing the screen using one of the Canon alternatives you have alter a setting in the camera to "tell" it which screen you have fitted.

Best of luck and report back how you resolved it.

Box Brownie wrote in post #4455805
Lastly, and if I understood your OP it is possible that replacing the screen has caused an issue (see my questions above) because on the 40D (1 series as well?) changing the screen using one of the Canon alternatives you have alter a setting in the camera to "tell" it which screen you have fitted.

I believe that CF setting allows the metering to compensate for the differences in image brightness between the different screens. Nothing to do with focusing.

Erm, unless I'm much mistaken, you can't change the focus screen on a 400D/XTi.

If you can, then I'm a berk as that's one of the reasons I upgraded from 400D to 40D.

EDIT: Just had a look inside my 400D. There doesn't appear to be any way of removing the focus screen and the manual makes no mention of it.

tzalman wrote in post #4456903
I believe that CF setting allows the metering to compensate for the differences in image brightness between the different screens. Nothing to do with focusing.

Fair comment as the screen is not in the AF pathway but as the 'new' screen would be a 3rd party like the Haoda one for the XT then it is remotely possible that in fitting it some misalignment has been caused to the secondary mirror??? i.e. user error hence my question to the OP about how the camera AF'ed before the screen was swopped over.

jemann wrote in post #4457989
Erm, unless I'm much mistaken, you can't change the focus screen on a 400D/XTi.

If you can, then I'm a berk as that's one of the reasons I upgraded from 400D to 40D.

EDIT: Just had a look inside my 400D. There doesn't appear to be any way of removing the focus screen and the manual makes no mention of it.

Yes same as my understanding ~ see my comment above ^^^

I think i AF'd fine, but i don't usually use AF except at weddings.

I think it might be the fact that i was shooting at f/2.8. I checked out the screen, and reinstalled it properly again, and focus is spot on. I don't think the screen had anything to do with it.

I think i need to start shooting at a larger f-stop. I figured it was probably user error, but wasnt' sure. The lens i was using is focusing fine.

Also, i noticed the center focus point seems to focus much better than the other ones. could have been an issues as well.