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How does micro adjusting work with zoom lenses? What if you have a lens that is not sharp at one end of the zoom range?
I think most cameras - ?maybe all Nikons - only allow you to set micro adjust at only one setting per lens. The advise I've heard is to set AFMA at the long end of the zoom. The rationale being, I think, that any out-of-focus due to not having the AFMA exactly on at the wider end of the zoom would be more likely to be lost by the deeper depth of field at the wide end. If that makes sense in how I explained it.
Some of the Canons allow you to set two AFMA points for a zoom lens, so you'd set one AFMA setting for the widest end and another setting for the longest end. So, of course, you end up testing two times for a zoom lens. Off the top of my head, I think Canon's 6D, 5D3, and maybe 1Dx allow this. What happens with one of these Canon's, I think, is that when you have the zoom set to a mid-point in the focal range, between the shortest end and the longest end, the camera will "guess" at the proper AFMA setting. For example, say your wide-end setting is "-10" and your long-end setting is "0", one of these aforementioned Canon cameras will guess a setting of "-5" at the mid-point range of the zoom.