AF Fine Micro Adjustment feature on 60D

Started Dec 31, 2011 | Discussions thread
kolas
Regular MemberPosts: 463
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Slow vs. fast lens
In reply to Jerry-astro, Jan 3, 2012

Jerry-astro wrote:

I've probably read more about 100-400 MFA issues here than most any lens, and that certainly was my own experience (mine requires +12 with my 7D). Feels like there's something about the design of that lens that seems to make it more susceptible to focus calibration issues.

The 100-400 is a relatively slow lens and that could be the reason it needs MFA to make it focus with pinpoint accuracy.

Simply put, the DOF wide open is wider than with a 2.8 lens. There is more latitude in front and behind the exact focus point where the AF sensor would still regard the object as in focus.

Phase detect AF is not searching for best contrast, it stops when it reraches acceptable contrast. It is designed for speed, not accuracy. Contrast detect AF in live view is more accurate but much slower.

Hopefully next generation cameras will be able to do MFA automatically by comparing PDAF and CDAF results. It should not be that difficult to implement IMO.

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