Originally posted by biz-engineer Thanks for the clarification. I own a K1 and I went through focus issues. Two practical things to consider with the K1:
- Area of PDAF points: K1 points are larger than K3 (AF module was borrowed from the K3, but to cover a larger frame without additional AF points). When focusing on a surface that is smaller than actual size of AF point, random error is introduced by the non overlapping portion of the AF point area and subject.
- AF systematic error require fine tuning (same as other DSLR).
In order to distinguish what is the problem you are having, use a good sized subject, if focus error disappear, then you've got to consider AF point area in your shooting, if focus error does not disappear, then you've got to go through a AF fine adjust.
---------- Post added 02-10-16 at 08:54 ----------
If you are doing portrait shot with 50mm f1.8 on FF ("focus on the eye"), then your camera is positioned at about 5 feet from your subject, in that case K1 is capable of focusing on the eye without error (except if your camera copy is out of spec). If you want to focus on the eye and have shallow DoF with the eye in focus, and you are 30 feet from the subject, in that case, the K1 AF point area is too large to focus on the eye, but anyway DoF is so large (even at f1.8) that whether you focus on the eye or on the head does not matter much.
To be honest, if your K1 is within tolerances, AF fine tuned, you should not have issues within realistic shooting distance (given focal length). Now , if you try to explore the limits of K1 AF capabilities by using uncommon focus conditions, you'll defeat it faster than with some other brands of cameras. I mean, as a photographer, the goal is not to use conditions to make the camera AF fail. The amount of sharp photos with tiny DoF that have already been posted by many K1 owners in various threads of Pentax forum (shot with 77 f1.8, 85 f1.4, 300 f2.8, 450 f5.6) bring some evidence that K1 AF works well including with f1.4 lenses.
I have sharp portraits wide open too, what I'm saying is that acquiring focus sometimes is an issue, with eye sharpness varying in the same set, with same parameters. I thought it's just the cheapo lens with the screw drive motor, but maybe it is the system, in that case I'm probably never going to achieve the level of fast and accurate focus that I had with my mft body which I didn't expect (I actually expected the opposite).
I'm not denying other spec improvements I got with k-1, images look great, noise level is incredibly low, dynamic range yada yada, all true. But since everyone in dslr world keeps crapping on mft bodies for their inferior focusing capabilities, especially tracking the subject, I thought a flagship dslr such as k-1 would show some improvements in that area too, which I guess it doesn't. I really should just rent a D fa lens and see for myself, people's reports even in this thread vary quite a bit.