The Zeiss Jenna 20/2.8 Flektogon is an amazing lens if you get a good sample. Some even say the center of that lens even rivals the Contax Zeiss 21/2.8 Distagon. Make sure you can test it first, or return it if not satisfied.
I own a Flektogon 2,8/20mm. The center sharpness at 2.8 is the same as at f8! At 2.8 the edges are soft, but at f8 i get edge2edge sharp pictures. Bought it for 150 Euro
As has been said before, if you get a good copy of the Flek 20 it's very good.
I have both the older 4/20 and the last 2.8/20 versions and would say, based on my copies, that the 4/20 is slightly better corrected for distortion than the 2.8 but is not quite as sharp (4/20 needs stopped down a bit more - it's also only single coated unlike the 2.8 which is MC.). The 2.8, although not quite as sharp as a 17-40L - like the 4/20 it needs stopped down a bit more, is more even across the frame unlike the zoom. This is again based on my particular copies of these lenses and usage on a 5D.
You can even get a Nikon 20/2.8 AF non-D for that sort of budget. Nikon users don't want them because they aren't the D version, but there's no actual difference between the two versions beyond a useless distance reporting [which is pointless on a lens which hits infinity just beyond 2m]. The 20/2.8 AF non-D is probably the best deal in nikkor 20's. It's the same optics as the AI-S or the AF-D at a significant discount over either.
Thanks for this topic. I've never used or handled a CZ lens before, they look like they'd be wonderful =) However, I do have a 20/3.5UD, and was wondering on people's experience with it? So far it looks good, on my 300D, but haven't received my 5D in the mail yet and just wondering about other people's thoughts who may have more history with the lens.
