I am posting this issue here as I figure there are more specialists browsing the alt lenses forum
OK I have a very strange one. A few days ago I cleaned my 5D viewfinder deeply, I removed the focusing screen, the "washer" shims and the SI plate. All good so far.
Today I tried an alternative lens and I am usually good at focusing by eye but when I came home all my shots were out of focus. OK maybe I am not that good I thought so I took a few shots with an EF lens and autofocus.
Much to my surprise I realised that when the AF is acquired the object on which the AF locked is blurred in the viewfinder, but an object behind it looks sharp. It's all in the viewfinder as when I view my pictures they are tack sharp at the AF point.
What did I do wrong? I tried adjusting the diopter, no effect. Could it be something that went wrong with the shims when I cleaned the beast? If so AF would be affected too, am I wrong?
As you stated, the VF and FS have NO effect/impact on AF whatsoever. AF sensors are located under the mirror. However to obtain accurate manual focus, the distance from the rear element of a given lens to the sensor MUST be EXACTLY the same as the distance from element to the focus screen (FS). ANY deviation and you get front or back focus and need to re-shim and test, rinse and repeat.
The 5D is infamous for having issues (it varies by body) when you switch focus screens, even to other Canon screens (@#$%), from the original one installed (and shimmed) at the factory. 1 series bodies do not.
It's true what you said Rob. I did not notice the issue until I switched the std screen for the Ee-D (with grid). I am sure it was there before, but less noticeable with the std screen. That makes me wander at what I read in another thread: the grid screen might be more sensitive to - hence more suitable for - manual focusing.
Lesson learned about the washers then and I'll be more careful next time. I have three of these in my 5D and two are extremely thin, very hard to get them back in there!
THe 5D washer in my camera is very thin as well. The trick is placing the washer into the focus screen cage area and making sure the washer will clear the top tab that holds the screen. Then insert the screen and close the system. The screen should push the washer into position. Look through the camera to make sure all is well. I have done this several times and it seems easier than trying to get the washer into position perfectly...
I tried adjusting the diopter, no effect. Could it be something that went wrong with the shims when I cleaned the beast? If so AF would be affected too, am I wrong?