Back / Front Focus

Registered: Aug 13, 2009
Total Posts: 475
Country: Canada

Hey guys, I've been having some issues with my 35mm I bought last year around this time. I thought it might be a front/back focus issue so I tried out a test.

It looks to me that its front focusing by a little and might be why I'm not seeing sharp images.

The lens is just nearly 1 year old, and I have it on my XSi. I'm in Canada and if it is something that would require calibration I wonder how it works up here in the north.

Looking for opinions on the test as I've never actually done it before.

Registered: Feb 19, 2004
Total Posts: 4081
Country: United States

I'm not familiar with that test rig of yours but where is your focus it the line where the little arrows are pointing to? If so, it's possible the actual AF point is picking up the signature just below it and skewing the results. That's why I hate these (and similar) focus test rigs as it's too easy to misplace the focus point. Focusing should always be on a completely flat area that is absolutely 90 degrees perpendicular to the camera/lens in both axis. When you introduce an angle that is too close to the area of focus, it could effect the focusing and invalidate the results.


Registered: Oct 09, 2005
Total Posts: 7450
Country: United States

Diagonal focus test charts don't work. I'll let you guys argue about it amongst yourselves.