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Yeah, as resolutions climb autofocus not being aligned exactly to the sensor is a bigger and bigger problem.

I have a very high res (mirrored) medium format system and keeping the “focus trim” set correctly to align the AF system with sensor seems impossible, seemingly changing with temperature or other conditions.

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> seemingly changing with temperature or other conditions.

Focus also shifts with aperture, it's impossible to have an open loop system that works accurately. Some lenses will front focus wide open, be spot on at f4 and back focus after that, or the opposite. Or be spot on wide open and oof when you stop down.

Also can change with what focus point is used, distance to the subject, focal length (for a zoom). It's a huge source of frustration, and while mirrorless cameras aren't perfect at this, they're so much better than DSLRs. I do still love the shooting experience of an optical viewfinder though.

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