Originally posted by kerey The same shot with the kit lens doesn't show this, although the DOF from that lens certainly makes the comparison more difficult. The M lens at 5.6 still exhibits a shift in focus towards the background. What's causing this? Poor technique? I'm pretty steady with the camera, and I certainly don't consistently lunge toward the subject as I press the shutter. I don't even know how this might be occurring optically. Any other users noticing this, or do I just need more practice with manual focusing?
This is one of the biggest failures of modern cameras. It isn't just Pentax - Canon and Olympus are notoriously worse in this regard.
The focus screens are made to focus and meter with the kit lens, which is a very slow lens indeed compared to your 50. It is even worse with my 85/1.4.
Unfortunately the only remedy is a dedicated manual focus screen (Pentax does not make one) or a split-prism screen which you can get from third-party vendors. The problem with the split-prism screens is that they mess up exposure. Pick your poison, I suppose.
Originally posted by Stratman Have you adjusted the diopter on your viewfinder? Maybe it got knocked off a bit, and you didn't know, it has happened to me a time or two !
If the diopter wasn't adjusted correctly, nothing would be in focus. It is the inherent DOF of the screen itself that can confound manual focusing with fast lenses.