Congratulations on your new K-3 and welcome to the world of picky technique. Soon after the K-3 debuted, this site had frequent new threads regarding disappointing (soft) results from the new camera. The causes may be summarized as follows:
- Any lapse in focus or deficiency in lens quality is much more obvious when pixel peeping a 24Mpx capture than at half that resolution (your K-x)
- Even a small amount of camera motion can be deadly
- Missed focus is much more obvious
The first point is simply a matter of perception. To screen for this, simply downsample the soft image to 12.4 Mpx and evaluate the sharpness of that version as if it were made using your K-x. The second is a matter of technique. I have learned to be much more aware of camera hold, bracing, and breathing in a manner similar to what I use with my film cameras. When using a tripod, be sure to turn SR off. I suggest using the 2s delay. Remote shutter release (IR or wired) may also be a good idea for some subjects. On the matter of tripods, it has been my observation that most people try to get away with support that is inadequate for their kit.
Now back to your focus issues. As I mentioned above, your complaint is not unique. I suggest the following before devoting (wasting) a lot of effort doing a valid AF fine adjust:
- Using a high contrast FLAT test target with camera on tripod about 20x - 40x the focal length distant, attempt manual focus using magnified live view. The purpose is to see whether your lens is capable of sharp results to your standards with the K-3. If not, you can stop here as far as that lens is concerned.
- The second step is to evaluate the PDAF system using the same set up and limiting yourself to the center focus point in AF-S mode. Reset the fine adjust to zero. Do 20 focus attempts, 10 racking from far-to-near and 10 from near-to-far. Of the 20, how many have obvious missed focus? Is that number unacceptably high?
If the answer to the last question is yes, the next task is to determine if the missed focus is due to poor precision (not something you can fix) or poor calibration (something you may be able to partially address with a fine AF adjust). I won't go into detail about how to do the fine adjust except to say that the matter of precision is important. Even if properly calibrated, it is unlikely that the PDAF system will lock to the same plane of focus every time in a test of 20 exposures as we did above. Ideally those results will be equally distributed on both sides of the desired plane of focus. In that case, there is no need or benefit in doing any fine adjustment. If more results focus behind the subject, you have backfocus. If the opposite, you have front focus. There are several ways to evaluate front/back focus with the most common being: a) some sort of scale/target device that allows easy visualization or b) use of magnified live view as the gold standard and observing the direction the PDAF moves the focus ring to attain its own notion of correctness. Either way, it is important to base the direction, amount of correction, and confirmation on multiple focus attempts. If you use a slant scale device be sure that the target is flat and parallel to the camera focal plane. Your intent is to provide an unambiguous subject.
Oh, and one other thing...it is fairly common for zooms and internal focus lenses to require different adjustment at different distances and/or focal lengths. That kind of adjustment may be done by the owner of certain Sigma lenses that support the USB Dock device, but for most lenses, a shop with the appropriate Pentax calibration instruments is needed.
Steve
Last edited by stevebrot; 04-11-2016 at 11:35 AM.