Originally posted by MSL Open mouth ... if it is the AF system's fault, wouldn't it also create problems with other lenses. Just to keep the comparison reasonably fair with two lenses of similar range and speed - I'll be a lot more excited about the images coming out of my F35-70/3.5-4.5 than the kit lens. It is like the sharpness and colors just aren't there with the 18-55.
it really depends on the circumstances. the "old" (pre k3) PDAF prefers hard edges such as reeds or railings, or perhaps in this case the snow, to softer, furred or feathers subjects. it's quite common for the AF to lock on a target half a frame away. maybe this is the first time he has actually notice the phenomena because of his subject matter.
it has everything to do with relationship of the edges to the intended target, focal length and aperture. maybe he's managed to avoid issues with greater DoF before. maybe his subjects haven't been animals that often and so they tended to fill the screen more.
we could spend hours investigating every picture he ever took to determine why he hadn't encountered this problem before, and we could come to different conclusions.
I KNOW for a FACT I have this issue with my K5iis and I have read enough posts by both forum members and others in the blogosphere that have documented this AF "quirk".
therefore, I have concluded this matches a characteristic tendency of Pentax DSLR that I have a lot of experience with.
why the OP never noticed it before is beyond the scope of this thread, if you are claiming that Pentax DSLR have no AF issues that's a different tangent.
I was offering my opinion of his dilemma based on my experiences.
yes, I agree the 18-55 is not pro quality glass, but there is a reasonable level of expectation of IQ that this presented image does not meet. I do not believe the kit quality IQ of the 18-55 entirely explains the poor image.
I own a DA 50-135, Sigma 100-300 F4 and a Tokina 80-200 f2.8. I can regularly and repeatedly recreate this exact same image with THOSE lenses while using the K5iis PDAF with center point only selection. I have seen this exact result (soft animal, perfectly focused sharp edged object in another part of the frame) many many times too often in my own images, much to my heartbreak and dismay. So I feel reasonably assured in my hypothesis that it is the AF system