This is my list for my K-mount cameras, indicating how I bought them, and my primary use:
- F 50/1.7 (used) - my reliable nifty fifty workhorse, which I bought because I liked the build better than the
- FA 50/1.7 (used) - now most times residing in my daughter's bag
- D-FA 50/2.8 Macro (new) - often used in documentary photography when I want the ability to go into macro ranges without changing lenses, or for digitizing negatives,
- FA 50/1.4 (used) - still not fully at terms with it, but after careful re-calibration of focus I'm trying to learn to use it more for it's smoother bokeh than the 1.7,
- Schneider Componon-S 50mm/2.8 (used) - by now inexpensive enlarger lens with outstanding resolution at f/4 around 3:1 magnification, reverse-mounted to Bellows-K for focus stacking,
- Pentacon-Six Flektogon 50mm/4.0 (used) medium format lens on a Hartblei Pentax-K tilt-adapter - for focal plane tilts when I have lots of time to compose and don't need to carry it far,
- Revuenon 50/1.7 (used) - my first K-mount 50mm, now usually on my Program-A, Cosina-built, superb mechanical quality, in need of some UV light
- Still 50-ish as in the original post, a Helios-44M4 58mm/2.0 with a permanently affixed K-adapter and hole for the mount pin for portraits on APS-C (K-5 with S-type screen).
Except for special uses, I recognized that I much prefer lenses with A-settings and thus have ruled out getting into adapted or legacy lenses any further for general photography.
I have a number of other ~50mm lenses in different mounts and look forward to clean and lube that Carl Zeiss Jens Biotar 58mm/2.8 on the Praktina FX, from which the Helios is said to have used the optical design. Others include various Praktica-B mount 50s, which have for a long time been my most used lenses and through which I acquired the '50mm-eye'.
I did buy a DA50mm/1.8, but sold the plastic fantastic later on because of the vignetting on my then new K-1 and the similarity to the F50mm/1.7. I thought of re-acquiring one for the KP for its light weight, rounded aperture and nicer manual focusing feel, but the above ~7 lenses already don't really see enough use.
I did not buy the DFA* 50mm/1.4
yet, because the 15-30mm was first in line during the last specials season and didn't want to be too greedy. The DA* 55mm/1.4 still looks interesting as a fairly universal, not too big and quiet-focusing replacement for at least the FA 50/1.4. I don't mind the whirring, but that 'Crack!' at the focus limits of the classic 50s is simply brutal. I'd still keep the compact f/1.7. The Sigma 50mm/1.4 HSM would be another contender, but given its size I feel it would just be an unnecessary step towards the close-to-perfect looking DFA* anyway. If I shall ever come across the Zeiss Macro-Planar 50mm/2.0 in ZK mount at a reasonable price, I'll for sure buy it. The regular 1.4 Planar however doesn't seem to exhibit the typical Zeiss character that much. Another dream with almost diametrically different character would be the Voigtländer Nokton 58mm, but I've almost given up on it as used prices have risen beyond reason. The remaining options with at least KA mount -Samyang 50mm/1.4 and Sigma 50mm/2.8 macro, don't seem to bring anything special to the table. Did I miss any other than the Pentax-A 50mm/1.2?
I have started a write-up of a subjective comparison of the 'classic' AF 50s (50mm/1.7, 50mm/1.4, 50mm/2.8 Macro, 50mm/1.8) backed by actual photos to illustrate their character. It was triggered by a number of questions on how they compare. Would there still be any interest?