Jim Meeks asked: "As a follow-up question regarding the best Pentax screw mounts, I've heard about Zeiss and other makers like Vivitar and Soligor. Do any of these lenses compare optically or in build? How about the new Russian lenses or Cosina/Voigtlander? Thanks again."
Jim, I have a great deal of experience with older third-party lenses and have amassed many pages of comments from various websites. I offer the following evaluations, from memory (some details may be slightly off): Vivitar's best lenses were designated Series One or Series 1. The Series One primes are the 28/1.9, 100/2.5 macro (1:1 magnification), 135/2.3 (1:4.5 magnification), 200/3 (1:4 magnification), 450/4.5 mirror lens (which you'll never find, and if you do, never afford), and 600/8 "solid CAT" lens. I believe all were available in screwmount, but only the 28/1.9 and (if available) 105/2.5 were multicoated in the screwmount version(s); the 135 and 200 were multicoated on the K-mount versions only. (Don't feel bad; some Series One primes for bayonet mounts like Canon and Olympus were single-coated.) These are the Vivitars to go for. The 105/2.5 macro is also sold as a Kiron 105/2.8, but possibly in bayonet mount only. Some non-Series One lenses are said to be as good as a Series One, notably the 100/2.8 macro (1:1), 135/2.8 macro (1:2), 28/2 macro (1:4?), and 35/1.9. I tested the 35/1.9 against the Pentax SMC 35/2K. It was no contest: The Pentax was much sharper in the corners at all apertures, at least as sharp in the center at all apertures, and at least as contrasty. As for the 28/2, I used to own its Kiron precursor (both were made by Kino Precision). It was as sharp as my Vivitar 28/1.9, but the colors were muted and contrast was deficient. Some of the Series One lenses were also marketed under the Panagor name. The 90/2.5 1:2 macro comes to mind. The Series One 24-70 f/3.5-4.8 was sold under Panagor or some other third-party brand whose name escapes me. Soligor's best lenses were designated C/D for Computer-Designed. The C/D primes included a 28/2, 35/2, 100/2 (the only 100/2 ever made in K mount, by the way); 135/1.8, and (later) 135/2.0; and 200/2.8. Most were available in screwmount. The finest-performing Soligor zoom was probably their 35-140 f/3.5 macro. Soligor images tend to have a green cast. Zeiss-specifically, Carl Zeiss Jena (CZJ) of the former "East Germany"-made several fine primes in M42 mount. The best were the 20/2.8 (multicoated), 20/4 (single coated but even lower in distortion), 35/2.4 (multicoated), 85/1.8 (multicoated), and 300/4 MC Auto Electric (arguably the finest M42 300mm lens ever made). The 20/2.8 and 85/1.8 use the same lens formulas as Pentax. The 20mm and 35mm CZJ primes focus remarkably close, typically yielding magnifications of 1:4 or 1:5. A 28/2.8 macro was also issued, but it was a rebadge of a Japanese lens. Among the M42 Russian lenses, the Zenitar 16/2.8 fisheye is no match for the older Sigma 16/2.8 fisheyes-at least no match for the Sigma XQ, which I own. Better choices would be the Peleng 17/2.8 fisheye or Mir 20/3.5, a rectilinear lens. The Peleng 8mm fisheye is fun to use. The Helios 85/1.5 is not that sharp but makes a superb portrait lens, which a many-bladed diaphgram that yields beautiful bokeh. Speaking of Sigma, their 21-35 f/3.5-4.2 is probably the finest wide-angle zoom ever offered in M42 screwmount. It was introduced even as Sigma introduced autofocus counterparts in the various bayonet mounts! Among third-party normal lenses in M42, the best is probably the Tomioka 55/1.2. But I doubt it's better than Pentax's later 50/1.4s and 55/1.8. Several 400mm German lenses were made in M42 mount. My favorite is the Enna 400/4.5 Tele-Ennalyt, a remarkably compact design. When you can find one, it's usually less than $300. I'm not aware that Cosina/Voigtlander primes are available in M42 screwmount; just Leica screwmount. Paul Franklin Stregevsky
