Back focusing on Pentax FA 50mm 1.4


sunface13

Link Posted 06/03/2009 - 10:00
I've just started noticing that my FA 50mm lens is focusing about 5mm-10mm beyond the intended focus point. Has anyone experienced this sort of problem with this or any other lens? Does anyone know of a way to correct the problem other than the rather hit-and-miss solution of focusing on something closer than the subject? I shoot with a Pentax K100D.

Any comments or suggestions are gratefully appreciated.

shim

Link Posted 06/03/2009 - 10:07
You haven't said if this is during AF or MF. There is another thread going on currently about MF problems. Basically I don't think you can do much about it except take a second shot from 10mm back (MF only) or use a small f stop.

shim

iceblinker

Link Posted 06/03/2009 - 10:09
If you're quite sure about the back focusing, and suspect it may be happening with other lenses too*, you could take the camera to a service engineer to be adjusted, or do it yourself:

http://forums.dpreview.com/forums/readflat.asp?forum=1036&message=22023704&chang...

* It may be not be so noticeable with lenses with smaller maximum apertures.
~Pete

shim

Link Posted 06/03/2009 - 10:33
Thanks for that link Pete.... I knew you could alter the K10 and K20, but didn't know the others can be done as well. I found with the K10 that the minimum adjustment brought me in front by 5-10mm which is actually worse because non of the object is then in focus and your out of range with DOF. It was also difficult with a focus rack moving in that direction (you had to set it up first) easier with back focus, just push the sliders as far forward as the will go focus and them move back 10mm.

shim

sunface13

Link Posted 06/03/2009 - 10:50
Thanks very much for the quick replies. I did a quick test with the kit lens and that appeared to be back-focusing too. So I followed the instructions on the link from iceblinker and it appears to be focusing accurately now. Thanks again.

iceblinker

Link Posted 06/03/2009 - 11:28
That's good to hear. Glad it worked
~Pete
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