Originally posted by cometguy 
What I don't get is that the pixel size in the KP is 61% smaller than the pixel size in the K-1. That means better resolution in the KP than in the K-1. Why doesn't Pentax use the same pixel size in the K-1, at least? I've not been able to find pixel size in any Ricoh literature or on the Pentax Forums specs for these cameras, so I calculated it myself. In astronomy imaging, pixel size is advertised on all cameras because it is extremely important. So the APS-C crop in the K-1 has lower (worse) resolution by a large amount (1.6x) compared to the full-size APS-C sensor in the KP. I want to know why, in a camera that costs twice as much.
There are pros and cons to smaller and larger pixel pitches, but a full-frame sensor trumps APS-C in image quality whether when you hold either megapixel or pixel pitch equal. It has either better data or more data with which to construct an image, respectively. Larger sensors cost more to source because they're made on wafers, like CPUs, and split up. Larger area means fewer sensors means you're paying a premium to Sony or whoever is manufacturing your sensor.
DSLRs are not primarily designed for astrophotography where pixel pitch is important because it is, in a sense, extreme macro photography. Dedicated astrophotography cameras also tend to use smaller sensors / image circles so that lenses have longer reach.
Post #9 by cometguy
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