[Oldbayrunner]

Very Simple, after years of using Apsc cameras I was ready to make the jump to full frame. Having a K3ll that I have been extremely happy with the KP was never an upgrade option for me.

[Fenwoodian]

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One can "split hairs" and discuss the technical differences between these two fine cameras. However, for me, there is only only consideration - BOKEH !

i've owned many Pentax APS-C bodies, and multiple copies of the full frame K-1. For my bokeh photography, I am able to achieve greater background blur with a full frame sensor. So, all of my wonderful Pentax APS-C bodies have been sold, and I exclusively use full frame bodies.


Note... I did recently purchase a K10D, but that was not for shooting, it was to conduct a comparison between CCD and CMOS sensors for a project I'm working on.

[Wheatridger]

From the K5IIs to the K3, none of my smaller Pentaxes have disappointed me for image quality. But I wanted a better OVF experience, and only the K1 give that. A bigger VF image beats a smaller one, every time, and with a DSLR, OVF size is a function of format size. The APS-C viewfinders were sufficient to frame an image, but the K1 offers a larger image that allows more study and enjoyment of the scene.

Advantage no. 2 is the Crop control given by the third topside dial. In an instant, I can make my lenses effectively 50% longer. This greatly enhances the utility of prime lenses, and enhances zooms, too. Yes, you can crop later, but it's better to have frame lines in the VF so you can assess the borders of the photos. For action photos, it can be helpful to see what's immediately outside the crop frame, so you can see what you're missing and what might soon enter the frame. Perhaps best of all, I can switch to Square and enjoy the classic pictorial proportions of my old Rolleiflex. When I try Square on a casual photo walk, the camera often stays that way.Compositions just seem to fall in place, and most all DA lenses become quite usable.

The combination of a K1 and an F2.8 zoom isn't comfortable for me; perhaps that's why I don't own any of those lenses. But it's amazing what you can do with small lenses like the FA zooms and primes.