Originally posted by rover ............a fast wide lens will be introduced by someone for the Pentax line in the next week or two? I think I can give them a couple weeks to design, plan, announce and begin manufacturing this new lens. Hey, maybe Pentax just forgot to put that new 20/2 on their lens road map and we will be surprised when they announce it. Let's not forget that Cosina can make it with or without Zeiss.
OK, back on this planet I do have a real hankering for that 20/2, fast wideish prime to lock onto the front of my K10D. My desire won't stay under control for long though. An A 20/2.8 or DA 21 may find it's way to me in a rush. I like my Tammy 17-50, but the zoom isn't doing it for me. I want something smaller, sharper, and still with speed. I know the DA is tiny, how much bigger is the A20? I expect the cropped sensor seeing only the center of the A20's image circle will help the handling of any distortion from the lens. How do these two lenses compare? I have read separately the praises of both, but are they comparable in performance to each other when compared directly? Used A20s still command a respectable price so the cost difference may not be great if I can find a nice 20. Am I missing any gems in my considerations? A 24/2 I don't know about? ( I would prefer something slightly wider than the 24/2.8 which is why I have not considered it.)
Oh, and thinking, I have not even thought of the FA lenses. Are they the same optics as the A series?
Well, the DA21 is a great lens, but it's not particularly fast f/3.2 and it has SERIOUS vignetting on 35mm film (and full frame sensors). Unlike the DA40 and DA70 that work fine with full frame sensors, the DA21 might be a bad choice if Pentax indeed releases a full-frame DSLR in the next 12 months and you want to upgrade.
The A20 (and FA20) are a quite a bit larger than the DA21 but they are both full frame compatible and can open up to f/2.8 when needed. Both are sharp and contrasty.
Sigma has the 20mm f/1.8 which is nice and fast, but there are some issues with that lens:
1) Barrel distortion (correctable in Photoshop)
2) Low contrast (correctable in Photoshop)
3) Soft wide open (fine stopped down to f/2.8)
4) Physically large and heavy lens (a little bigger than the FA20 and MUCH bigger than the DA21)
On the other hand, the Sigma is cheaper than the FA20 (if you can find the FA20) and you can open it up to f/1.8 if you're in low light and are willing to sacrifice a little sharpness.
Personally, I like the Sigma 20 better than the DA21 ... but I like the FA20 better than the Sigma.