Pentax K mount
The longest-lived mount still in production: every K-mount lens since 1975 fits every K-mount body, and because stabilisation lives in the body rather than the lens, all of it is stabilised. That is the entire argument for buying into Pentax, and it is a good one. The catch is that Pentax is the last company building SLRs — Sigma and Tamron both stopped making K-mount glass in 2019 — so the lens pool is what it is. Read the body notes before you buy anything from 2010 to 2013.
33 bodies and 95 lenses and 1 accessory tracked. Lowest used prices pulled daily from the major used-gear sites.
Full frame
2 modelsPentax took until 2016 to build a full-frame body, then made the sensor move: the K-1 shifts it for Pixel Shift, for AA-filter simulation, and for Astrotracer, which follows stars well enough to shoot minutes-long exposures without a tracking mount. Nobody else does this.
The solenoid years (2010-2013)
4 modelsThese four share an aperture-control solenoid that sticks with age and returns black or wildly overexposed frames. It is common enough to assume any untested copy either has it or will, it is a bench repair rather than a wear item, and sellers do not always disclose it. Test at f/8 before money changes hands. The K10D and K20D have a related failure; the K-3 generation onward does not.
Weather-sealed bodies
15 modelsSealing is where Pentax has always undercut everyone: the K200D put 60 seals in a consumer body running AA cells in 2008, and the K-70 and KF still deliver a fully sealed camera for entry-level money. The K-3 Mark III has the best optical viewfinder ever fitted to an APS-C camera, and its Monochrome sibling has no colour filter array at all.
Unsealed and early bodies
12 modelsThe 6MP *ist and K100D generation, the AA-cell consumer bodies, and the K-01 — Marc Newson's mirrorless K-mount experiment, which kept the flange distance and so ended up DSLR-sized with no viewfinder. These are cheap now, and the *ist family in particular is worth having only for the lenses it takes.