Originally posted by Digitalis i don't know if that is the worst, the optical performance of the SMCP-K 24mm f/2.8 leaves a lasting depression. Which is probably why the lens never made it to the M lens line up, despite its small size.
It made it up to the A series... Same optics.
Yes it's a lens that is weak in the borders, but I think it was created as an alternative to the larger/slower K 24 3.5... it was created and meant for a time before test charts were all that matter. Some older photographer views on it (from stans-photography.info):
Yoshihiko Takinami - "very sharp, good color saturation/rendition, scarce distortion"
Paul.Stregevsky - . . . "The lens makes me look like a better photographer than I am. What color! And it feels oh so nice in the hand. . ."
I had what I believe was a good copy of it and it was capable of taking very nice pictures, even wide open, especially at closer range. At a longer range sometimes if felt like it wasn't quite as sharp, but it was still very acceptable for me - I don't usually do much pixel peeping. The colors were fantastic and I actually miss that lens more than I thought I would - I traded it for a Cosina made Vivitar counter part because it allowed me to also get a Pentax-M 50 f4 Macro. The Cosina/Vivitar is just as sharp - maybe even a bit sharper, it's a good design from that standpoint, it was even sold branded as a Zeiss Jena. But the colors aren't nearly as nice, and the flaring/loss of contrast in bright situations kind of takes the joy out of it.
Regarding the A 28 2.8... I've had it and wasn't awed by the pictures I took with it under f5.6. From f5.6 on, very sharp and contrasty. But I had a Rikenon 28 2.8 XR that was sharp and contrasty wide open, so I sold that (and also the Version 1 M 28 2.8, which I actually liked better than the A version).
Now recently I got the Sigma 30 1.4 Art so I'm mostly set in that range. I did consider the F 28 2.8 as well, but now that the Sigma 30 1.4 Art is selling used in the 300 dollar range, I don't see why even consider the old F and FA 28 2.8 anymore, unless you need full frame of course, and can't afford the FA 31.