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Jonas is correct. AF adjust has NOTHING to do with manual focus. Nada. Zippo.
Accurate MF relies on the distance from the rear mount of the lens to the sensor being EXACTLY the same (did I say EXACTLY?) as the distance from the rear mount to the focus screen.
If they are off even a minisucle amount what looks in focus via the VF you won't be - the plane of focus will be just in front of or just 'behind' the plane of the sensor.
For manual focus lens users, the 5D (and by logical extension the 5DII) is infamous due to loose manufacturing tolerances for needing to have it's focus screen re-calibrated IF the factory installed focus screen is replaced with ANY (as in ANY) other focus screen -- INCLUDING any focus screens sold by Canon.
Because of manufacturing tolerances, the degree of re-calibration required, like the mirror clearance issue, will vary on a body-by-body basis. You'll also need to test/re-shim/test/re-shim/test EVERY time you change screens.
Shims (obtained from Canon Parts) can be changed (thicker/thinner), removed or you can use thin strips of scotch tape or metallic duct tape on the edges of the new screen in lieu of adding shims. You can also send the camera and new screen (Canon only of course) to Canon for calibration as well - but you'll do a better job yourself.
Because of tighter manufacturing tolerances, 1 Series bodies don't have the same issue. You can change focus screens 5x a day in any one them with no issues.
Edited on Dec 16, 2008 at 08:57 AM · View previous versions
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