Originally posted by Ash So let's say we're just looking at IQ at 20mm. At f/5.6-f/8, why does the 20-35 trump the 20?
Resolution wise, the FA 20 is better until F/5.6, especially in the corners. The FA 20-35 is no slouch either, but the corners are mushy wide open at F/4. They get better at F/5.6 and it's at F/8 - F/11 that sharpness gets optimal over the whole frame.
Surprisingly, distortion is a little bit better on the zoom and a little worse on the FA 20 (at least on crop format according to Photozone reviews
here and
here). Anyway, the distortion is normally not an issue with either lens on full frame, except when you have straight lines running near the edge of the frame.
Microcontrast and color rendering are a big advantage of the FA 20-35, which exhibits brilliant colors and constantly delivers punchy images. It has also a much greater resistance to flare when the sun is in the frame or just outside the frame.
Vignetting is present on both lenses when used wide open but becomes nearly invisible at normal landscape apertures of F/8-F/11.
Both lenses tend to suffer from lateral chromatic aberration (which is easily correctable) and from purple fringing on bright edges when used at faster apertures (this is more of a nuisance).
As a whole, I would say it's easy to pick the images from the FA 20-35 because they consistently look better when you see them next to the images from the FA 20. Technically, the FA 20 might be the sharper lens, especially when compared to the FA 20-35 at F/4, but at the apertures normally used for lanscape (F/8 - F/11), the FA 20-35 simply delivers better looking images.
Here's a quote from an
old Shutterbug review of this lens:
Quote: From f/5.6 to f/16--the most commonly used apertures with wide angles--the zoom produced highly satisfying slides at every focal length, suitable for a fine 11x14 print or a double page magazine spread.
Cheers!
Abbazz
[EDIT] I just noticed the FA 20-35 is still listed on Ricoh-Pentax Japanese website:
http://www.ricoh-imaging.co.jp/english/products/lens/k/wide/smcpentax-fa20-35/
It is still available new at their online store for ¥ 80,750 ($ 678) without taxes:
http://store.ricoh-imaging.co.jp/g/gS0027960/