What are the « C » ZM lenses?
Compact or Classic, Zeiss means both with the “C” prefixed to the name of these three lenses. Two of them are conservative designs (conservatively specified) that perform spectacularly well compared to their competitors. The third is a compromise between speed and size that brings an old-school look to images.
All three are reformulations of time-tested designs that span half a century of Zeiss lensmaking. Simplicity is making a come-back.
(I'm sorry I lost track of the original owner of these photographs... otherwise I would credit them.)
Carl Zeiss 4.5/21 C-Biogon T* ZM
The story of the C21 is twice overshadowed: first by the excellent 2.8/21 Biogon and second by the well-known 2.8/21 Distagon. The C21 is every bit a match for these two in the field. Distortion is essentially absent at 0.2%, which is a major plus over its two sisters.
The C21 invites comparison also to the new Leica 3.8/24 Elmar and 3.8/18 Super-Elmar lenses. Both Leicas deliver slightly superior numbers than the C21, but come with 5-10 times more distortions. The Leicas cost 2-3 times more and weigh 25-50% more than the C Biogon.
The pick? Both the Biogon and C-Biogon are really good values. The 1 and 1/3rd stop advantage of the Biogon (not C) is very compelling, but you can stack 2 C-Biogons in the same same volume. For a compact kit I would get the C-Biogon, and enjoy the low distortions. Still, it’s a tough call, (free) aperture is very appealing.
Carl Zeiss 2.8/35 C-Biogon T* ZM
The C35 weighs 200g and extends about an inch in length from the flange. As compared to its larger 2/35 Biogon sister, the key difference is the 30% - 40% shorter barrel. Performance is in most ways equivalent between the two for the overlapping aperture range. Distortion is very low at less than 1/2 of 1% at the corners, though the 2/35 surpasses it here with essentially zero distortions.
The C35 is only 1/3rd of a stop slower than the closest comparable Leica, the more expensive 35mm Summarit. Here this little gem far outclasses this rival in performance. Field coverage extends all the way into the corners of 24x36mm image sensors even from full aperture, and delivers essentially perfect results at f/5.6.
Again the verdict is difficult. The C-Biogon achieves identical performance as the Biogon (not C), in a smaller package and with 1 stop smaller aperture. The size difference isn’t as startling as with the 21mm, and the faster lens has less distortions to boot. I would probably pick the 2/35mm Biogon.
Carl Zeiss 1.5/50 C-Sonnar T* ZM
The C50 is a high-speed lens compressed into a very short barrel. It is probably the smallest lens of its speed class, which comes at the expense of micro-contrast somewhat. This gives the C50 a different look, like an artist that draws with charcoal until f/4 and fine pencil beyond. For this reason the C50 is perhaps the less obvious choice among the “C” lenses.
The 2/50 Planar is made with the same length, but lower weight, girth and price. The Planar also delivers superior performance across the overlapping aperture range. There is little to fault the Planar except slightly disappointing distortion figures (2%).
The Leica 50mm Summarit is only slightly more expensive than the Sonnar, but much smaller in every dimension. The Summarit performs the same as the Planar, for all intents and purposes, but with more subdued distortions. Among the three the Summarit appears to be the best performer, but also the slowest, at f/2.5.
Here I think the choice is easy. I would pick the Planar. I confess it is the least sexy of the three, but it is a sound value and compact to boot.
I started out deeply enthusiastic about the "C" lenses, but now I think there are better alternatives. Yes, they are the most compact, and they are excellent. But I'm likely to take a slight bit more bulk (like 30 grams) for that extra stop of light in most cases.