As a recent convert from Sony to Pentax, I have been anticipating the K-1 with so many features intended to astrophotography and night landscapes. However, I have been spending my first two weeks fighting an INFINITY FOCUS PROBLEM. Apparently, from forum and user group messages, this problem is not uncommon and has been noted by other pentax users.
PROBLEM: many K-1 bodies using many popular lenses cannot achieve proper infinity focus. The problem may not be apparent in everyday photography, but when pointed to star fields, the inability to achieve critical focus is obvious and apparent.
TESTING: While not a statistically valid sample, and not a rigorous test procedure, I have tried three different (new) K-1 bodies and several different lenses. Two of the three bodies could not achieve critical focus at all. The third was better, and perhaps even OK. Several different lenses were used to make sure that it was not a single defective lens. These included a 14mm Rokinon, a 35mm Pentax DA, a 50mm Pentax manual focus, a highly regarded135mm F2.4 SMC Pentax, etc. In general, of course, the longer the focal length, the more obvious the problem.
In most cases, I also took companion images with a Sony A7S, using similar exposures and lenses, to make sure that it was not a sky conditions problem. Both sensors are similar in size, although the K-1 has three times the resolution. Some of these images are shown below.
CONJECTURE: although I am a mechanical engeer mostly involved in software nowadays, i have no direct knowledge of Pentax designs or functionality. But, I have heard that some users can resolve the problem on some lenses by move the infinity focus stop on the lens - this works with Rokinon manual lenses, etc. So, this would seem to point to a misalignment of the sensor board within the camera body; possibly a manufacturing tolerances problem rather than design, pe se.
CALL TO ACTION: Pentax needs to do something! This is an astrophotography oriented camera that can't focus properly. I am sending a copy of this letter to Pentax USA. If you are having a similar problem, then you should too.
As for me, I give up. I have invested more than $2500 and two frustrating weeks trying to pin this down. I am going to return the body to poor Samys Camera, if they will let me do so, try to resell or return the lenses, and go back to SONY ...
IMAGES:
It is difficult to "match" images when the sensor resolutions are so different. I gave up trying. You only need to spend a little time looking at the Pentax monitor in LIVE VIEW to know something is wrong.
Pentax (Body 3, 7/20/16):
{it is a pain to show image on Pentax Forum, so please refer to:
Open Letter to Pentax - K-1 Infinity Focus Problems: Pentax SLR Talk Forum: Digital Photography Review