Does my 20d have a focus issue?

Hi,

A couple of months back I sent my 70-200mm to sigma due to softness, after phoning them today and contemplating the possibility of them sending me the lens back and me having the same problems I explored the idea of my camera having a focus issue.

I conducted a fairly simple test, a couple of shots of a ruler from a very, very low angle. I found that the manual focus shots were more in focus and the difference very minimal, would this kind of difference explain the softness I was getting at 2.8 200mm in real world situations? I must admit I've never noticed softness with my 38-76mm at 5.6.

The focus point was on the 'E' at roughly 25cm along the ruler. Picture 1 is auto focus picture 2 is manual.

Cheers for any input.

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i'd imagine these are 100% crops as it is terrible quality, in which case this is not a good test. the focus point of your camera is much larger than the E on the ruler. the af of your camera cannot focus on something that small accurately unless it is considerably higher contrast than the stuff around it.. which it is not.

if you want to do a test like this use a focus chart. i wouldnt bother though... if you dont notice it when you;re out shooting then its not a problem

Yes the pictures are bad quality, my question is though can that much of a difference (about 3 mm from a very low angle) make a 200mm lens at f/2.8 appear soft? If it can, I'll conduct a more accuarte test if not I'll forget about it.

You'd be hard-pressed to make a determination from that particular test. Remember the actual focussing sensor extends well past the indicated square on the viewfinder screen, and with an f/2.8 lens it's a cross-type sensor in the center. There's a chart (and directions) for a more precise test, with less room for error (if directions are followed precisely) that's been talked about repeatedly on here. If you get caught up in one of the various test methods which use offset batteries or books or tapes, make sure they're separated far enough that the AF point won't overlap 2 or more of them.