Contax G Carl Zeiss 90mm f/2.8 Sonnar – Conversion to Leica M


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Carl Zeiss 90mm f/2.8 Sonnar lens from the Contax G camera system.
Not sure what can be said about this lens, other then to make another one like this wont be possible!

This lens, uses a Leica 90mm APO 11636 “Black Lacquer and Solid Brass” Leica helicoid. We have tried to use various legacy/ vintage Leica helicoids to convert the 90mm Sonnar lens (trying Elmarit, Elmar, Summicron Pre-ASPH, etc.) and none worked as the CG90 formula has a rather short registration distance. Long story short, we acquired a 90mm APO helicoid lower, which actually had a short enough registration distance to work with the CG 90mm lens.

The next step, was to design a new optical block and aperture control system, that used the original glass elements from the 90mm CG lens, into an optical block that could install into the 90mm APO body. The new optical block also required the glass elements from the CG90 lens be optically compressed into an effective focal length tolerance that matched the Leica APO helicoid exactly. This type of engineering (optical compression, designing new optical blocks, machining new aperture control mechanics) we specialize in, but it does not come cheap. Often +/- 0.015 tolerances are required on various components, which require specialized manufacturing equipment to make.

The new optical block’s exterior mechanics were finished in gloss black lacquer to match the 90mm APO body lower. The CG90 hood was also repainted to match. The aperture ring was then engraved with the appropriate markings.

The end result is a beautifully built, one-off 90mm Sonnar lens for usage on Leica M cameras, that is fully RF coupled and focuses accurately. No funny plastic parts, crazy adapters or half-way measures were used to make this piece you see here. Considering we have had the other 90mm CG conversions here to compare against, we can honestly say this is the only 90mm Contax G conversion we feel has ever been done properly. But alas, as we don’t have additional 90mm APO 11636 helicoids here either, this may be the only one we do like this.

As to the optics of this lens, there are some coating marks on the front element, in the far corner. This does not affect the image quality at all. Lens has a 6-bit coded mount.
There are some minor marks on the black lacquer paint finish, both on the new parts and the APO helicoid lower.

Lens comes with a front cap, rear M cap, and a screw on black lacquer matched hood.

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