Focus help: 50mm f1.4

[Chazs]

Sorry if these threads are getting annoying, but I just gotta know!!:oops: :evil:

I know there has been a lot of discussion about front/back focusing of various lenses. I did a crude test with my 50mm f1.4. This shot was taken at 400ISO, 1/800s, f/1.4. Newspaper was about 18 inches away at about 45 degrees. The screen shot is from the EOS viewew utility showing the center focusing box (all the AF boxes had identical results.) Obviously the focus point is a wee bit off (about an inch). Is this an example of needing the camera and lens calibrated, or is this a trivial amount. At greater distances I'd imagine the problem to not be noticble. But for up-close work it could get annoying. Any thoughts on the significance of this? Thanks in advance.


http://home.wavecable.com/~stevensc/photos/lenstest.jpg

[tim]

Do a proper focus test (http://www.canon-dslr.com/Canon_Jan05/Canon_SLR_Focus_Test.htm), on a tripod, with mirror lockup and cable release, ISO 100, centre point AF. I don't have time to explain how a camera focusing system works, which would explain why you need to do what I said above, but if you could read this (http://www.fredmiranda.com/forum/topic/241524).

PS not trying to be rude just busy at work looking in on the forum :)

[tim]

Also, do "best of 5", and make sure you manually focus on infinity between each test.

[blue_max]

With such a slim focus depth, just the action of depressing the shutter could push the tip of the lens down a hair and move the focus point. Try auto focussing and then see if you can focus better manually. I find it hard to improve on the auto focus.

Graham

[rent]

assuming proper testing (follow tim's excellent link), and this is the kind of results you get, then yeah, it looks like it's front focusing a bit.

this could mean either your lens, or your camera, or both require calibration. if this is the only lens in your lens collection that exhibits this, then it's probably the lens. if all your lenses front focus, then it's probably the camera.

but yeah, do a proper test first.

-alex

[tim]

assuming proper testing (follow tim's excellent link), and this is the kind of results you get, then yeah, it looks like it's front focusing a bit.

You like the link? Great! I have others ;)

http://www.normankoren.com/Tutorials/MTF5.html
http://md.co.za/d70/chart.html