Originally posted by texandrews if you are looking into the " experienced " lens market
1 don't forget to look at the Forum's market place
2 regarding the Pentax 100mm macro F2.8 " family "
the same optical glass is shared by the F, FA, D FA ( non WR ) and D FA WR lenses
each " member " will sell at different levels if you can find them
check the In Depth Review of the D FA 100mm Macro F2.8 WR for confirmation
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remember that lenses developed in the Pentax 35 mm SLR " film " era were developed for the full frame sensor size you find in the K 1
this link shows the differences between each of the various Pentax lens " families " :
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 . . .
Pentax K-Mount Lenses Explained: The differences between various Pentax lens series