The M 50/1.7 and A 50/1.7 are among the most loved Pentax lenses for their performance and value for money. Users also admire the build quality of the M series lens and the useful "A" setting of the A-series.
So I thought I'd produce the perfect hybrid...
This task took longer than I'd anticipated because the two lenses, both in great condition, produced noticeably different results using exactly the same settings. The M-series lens was slightly sharper in the middle (but only if you pixel peep on the computer). The big difference was that the A-series rendered more accurate colours. Differences in the two unprocessed images at ISO400, f11, 0.4" can been seen below.
Overall, I prefer the A-series 50/1.7 for its colours and ease of use...and perhaps I'm lucky as my copy does not have the wear and tear problems with the aperture ring some have experienced. Both are great lenses but the A is the one I'd recommend first.