Originally posted by PALADIN85020 In short, with my APS-C lenses, I might be better off taking pics with my K-3 than the K-1 in cropped mode. Am I wrong? I have an investment in APS-C lenses, and I would want to use them to the best possible advantage.
There is also the possibility of simply going manual crop with the K-1 - using your APS-C lenses in FF mode, seeing what works (or not) and what aperture or focal length gives you results you are happy with, and then manually cropping the 36MP image to suit (if needed).
Some DA zooms may need this sort of approach more than primes, as they may (for arguments sake) vignette very heavily at wide zoom, but work fine at normal or longer zoom, and so produce fine 36MP images at those longer focal lengths. If you relied on the camera to just apply auto-crop to such a DA zoom, all you would ever get is 15MP images, and miss the chance for lots of problem-free 36MP images.
Unless, of course, the Pentax 'Auto' crop function is smart enough to selectively crop a DA zoom lens only to the focal lengths where it is needed - eg for the DA 17-70, 17mm = apply crop, 30mm= apply light crop, 50mm and above = do not apply crop. I doubt this will be the case, however.
So IMHO just shooting 36MP all the time, and manually cropping, may in general be the best way to go, particularly with DA zooms. (And for non-Pentax crop lenses the camera may not have in it's database].