jimmy462 Offline Upload & Sell: On
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Cary Smithson wrote:
Long time lurker who upgraded from a 7D to a 7D2. Could not get any sharp shots with my 70-200 2.8L IS II on the 7D2 no matter how I tried to micro-adjust it. I usually shoot little birds at f/2.8, center focus point. Even shooting very high shutter speeds, on a bright sunny day, every shot was still soft. It was inconsistent, sometimes front focused, sometimes back-focused, but never a tack sharp shot. However, when I tried shooting at f/5 and above, all of a sudden, every shot was tack sharp. Can somebody smarter than me explain why? I don't think I "fixed" the problem, but it'll get me through airshow season, then I can send it in to CPS afterward....Show more →
Hi Cary,
The short answer as to why f/5 is yielding more consistent results than f/2.8 is that your depth of field (DOF, henceforth) at f/5 is deeper than at f/2.8. The deeper the DOF the better the chance of getting your subject in focus.
Here are some example DOF numbers for shooting a "little bird" at 10 meters...
200mm @ 10 meters @ f/2.8 with a 7D2 = from 0.13 meters in front of the little bird to 0.13 meters behind the little bird will be in focus. Total DOF = 0.16 meters.
200mm @ 10 meters @ f/11 with a 7D2 = from 0.5 meters in front of the little bird to 0.56 meters behind the little bird will be in focus. Total DOF = 1.06 meters.
Oh yeah, and your f/5 shots work out thusly...
200mm @ 10 meters @ f/5 = 0.23 meters in front, 0.24 meters behind for a total DOF of 0.47 meters! F/5 is more forgiving than f/2.8!
Here's a nifty online calculator to play with to get familiar with these concepts...
Online Depth of Field Calculator:
http://www.dofmaster.com/dofjs.html
I hope this helps!
Jimmy G
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