RDenney - I have a Zeiss Jena DDR 20/2.8 that is quite sharp from one corner to another, at least on the 1D II (not tested yet on full-frame). But it does lack a good deal in terms of contrast, at least compared to the 16-35L. It does have that very smooth operation that is a signature of older, well-machined lenses.
I intend to test it fully when I get a mind to do so.
I didn't say they weren't useful in the wide range, I just said I thought it more likely that the Pentax lenses would perform better. For example, I'll bet that a Pentax 20 (if one existed which I don't know) is as sharp as your CZJ 20, but with higher contrast. I'm basing that on two things: 1.) the Flektogons in medium format are competitive with old lenses, but do not have the performance of modern wide-angle lenses in terms of sharpness, color rendition and contrast. And they also seem to vary quite a bit, with one being though excellent and another howling at the moon. I have two 50mm f/4 Flektogons for the 6x6 format, and have tested one in detail. It's very sharp in the center, quite soft at the edges, and not particularly rugged. For many subjects it is fine, but I would rather use my Pentax 645 45-85 zoom lens for taking a large group portrait where I wanted all faces to be clear right to the edges.
2. There are no wide-angle lenses from the 50's and before that are really the match of more modern wides. Partly this is because of coatings, though both my medium-format Flektogons are multicoated. Partly it's because of design--those designs come from before computer design, the use of low-dispersion glass, and the ability to grind or mold aspherical elements. A key factor is how important it is for the elements to be centered and collimated with great precision, and despite the German reputation for precision, Carl Zeiss Jena was still a state-run factory in a communist country, and quality control is high only by Soviet standards. I doubt the Takumars of the 70's have low-dispersion glass or aspherical elements, but they certainly benefitted from the ability to run the math on computers and they also benefitted from far better and more consistent construction and truly superior coatings.
Rick "whose Ukrainian 45mm medium-format wide-angle lens has excellent contrast but poor sharpness--the opposite of Zeiss Jena" Denney
