Welcome to the forums
lots of friendly members eager to advise you on how to spend your money
may I suggest that while you wait for more responses, you go up to
" Cameras " above and look at the
" User Reviews " and the
" In Depth Reviews " and take a look at the various Pentax cameras there
Pentax Digital Cameras and Film Cameras - Pentax Camera Reviews and Specifications Pentax K-3 II Review - Introduction | PentaxForums.com Reviews Pentax K-3 II - Pentax K-mount DSLRs - Pentax Camera Reviews and Specifications
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you can use the tool found there which allows you to compare cameras side by side
https://www.pentaxforums.com/forums/pentax-cameras-compared/?c1=Pentax+K-3+I...3=Pentax+K-500
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by going to
" Lenses " you can do also look at similar reviews for
Pentax Lenses and
Third Party Lenses as well
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additionally these charts might be of help
Pentax Lens Compatibility Chart
Copyright 2006-2016 Mosphotos.com. All rights reserved.
Pentax bayonet lenses labeled "SMC Pentax" are referred to as "K" lenses in the table below. Other Pentax bayonet lenses have the lens designation as a part of their name as in "SMC Pentax-FA."
Note that "star" lenses work like their "non-star" counterparts: DA* lenses work like DA lenses, FA* like FA, F* like F, A* like A, and M* like M.
Exceptions: FA and F "soft" lenses behave like M lenses in terms of metering.
http://www.mosphotos.com/PentaxLensCompatibility.html
Pentax K-Mount Lens Series Explained: The differences between various Pentax lens series
In a nutshell
There are several series of Pentax K-mount lenses; the ones currently being produced include the DA (digital), DA L (cheap digital kit), D FA (full-frame, digital optimized), and FA (full-frame) series. While all Pentax K-mount lenses ever produced are compatible with all current Pentax DSLRs (in some cases with restrictions in that not all exposure modes of the camera are supported by old lenses), there are significant differences between each lens series and each has different features. Furthermore some of the newer lenses do not work with older cameras. We'll be exploring the differences between the various K-mount series lenses in this article. Read more about specific K-mount lens/camera compatibility here.
The DLSR designation below encompasses the mirror-less K-01.
http://www.mosphotos.com/PentaxLensesExplained.html