Originally posted by roentarre ...
A 50mm f1.2 requires an effort to try to use. I often carried it with my travel but its keeper rate with wide aperture gets about 1% keeper rate. All pentax 50mm has the same sharpness at f2; so buying this lens needs justification.
I know this lens and it is a great one.
I think part of your low success rate is with focussing a manual focus 1.2 lens with an autofocus digital SLR. Most digital SLR's are poor manual focussing tools when it comes to this kind of precision.
I have a Canon 5D and a converted Takumar 50/1.4 and a Rokkor 58/1.2 (fabulous lens by the way) and obtaining good focus wide open was a pain. Most digital SLR's come with bright viewfinder screens. But they have very little matte in the screen which makes it hard to tell if subjects are in focus or not. Shooters who use fast manual lenses will use a darker matte screen for better accuracy. Quite often the shims that hold the screen in place need to be adjusted or even replaced with a shim of a different thickness. This can take some trial and error. The downside is that these screens will be darker which can be a negative factor indoors.
Do a focus test: shoot a measuring tape(near to far) with the camera on a tripod with the lens wide open. Focus as carefully as you can. Then view the results on a good computer display. I bet your camera is either back focussing or front focusing by an inch or more. At f/1.2 this can make a big difference. So, my hunch is that the 50/1.2, a superb optical tool, is showing the weakness of the loose factory specs with regards to manual focusing on your camera. Remember the auto focus and manual focus are two different systems on a modern camera. I bet a good copy of a Pentax LX, with a matte screen will give a much, much higher success rate with the 50/1.2 than you are getting now. The difference is the LX was a precision manual focusing machine and the modern digital SLR (almost all of them) is much less so...
Cheers,
Max