The Usage and Limitation of Group AF

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yihlee
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The Usage and Limitation of Group AF
2 months ago

About Group AF (I would rather just call it 'd5'.)

'Group AF' provides four backup focus points. If, for any reason, my chosen point fails, one of these backup points may pick up focus lock.

How about missed focus - focus does lock but it's locked on something I don't want?

Look thru viewfinder, those 51 focus points are physically 1 to 2mm apart from each other. How does those 1~2mm translate to real world distance? For a head/shoulder shot, it's 3~6cm; for full body shot, it's 20~40cm.

If I'm shooting head/shoulder and missed the eye, d5 may pickup the nose or ear. Is it good enough? Of course. It's always better something than nothing.

Now if I'm shooting full body aiming at the face and missed it, those backup points from d5 may pick up something 20~40cm apart - I'll be lucky if it pick up the person's belly. But more often than not, it would just focus on something I don't want.

To summarize: To use d5 effectively, the core elements of my subject should occupy an area that is bigger than d5's coverage.

Of course, we can always leave Nikon out of picture - using manual focus. But we all know it's just not possible sometimes.

Here's couple examples where 'd5' might save the day.

Would 'd5' hit it where 's' failed? Maybe, maybe not.

'd5' definitely would score a hit where 's' failed.

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