More lenses for a Tenax II

28mm f3.5 Auto Nikkor lens on a Tenax II. Finder is correct one (432/6) for the 2.7cm Orthometar

Rangefinder cameras and wide-angle lenses are an excellent combination. But what is a Tenax II user to do when the only wide-angle lens was a 2.7cm f4.5 Orthometar of which only 302 were manufactured? That is 1/10th the number of Orthometars made in 35mm for the Contax! But it appeared that there might be enough room to fit a Nikkor lens in F mount on a Tenax with the proper adapter.
I watched ebay and was finally rewarded with a lens mount for a 4cm Sonnar missing its optics. I took this lens mount and a Nikon K3 ring to a friendly machine shop and a month and a small fortune later, I had an adapter that will allow the mounting of some Nikon F mount lenses. I say "some" because while the bayonet mount is perfect, many Nikkors project beyond the bayonet flanges. Far enough and they hit the rear of the adaptor.
What works? A early  (non-AI) version of the 105mm f2,5 Auto Nikkor works fine. It appears that it might vignette only slightly. But what I wanted was a wide-angle. An early version of the 28mm f3.5 Auto Nikkor looked like it might work except for the back flange extension designed to protect the rear element of the lens.
 Two hours of careful filing and fitting, and the 28mm Nikkor fit. When combined with the proper 2.7cm Zeiss finder for the Tenax, I was all set. Except for lack of rangefinder focus and its size, it is a perfect combination. And it does not vignette.

Back of the adapter. Beautiful machining including a new latch.

Adapter front.

Our gate, taken with the 28-Tenax II Combo

Our backyard, taken with 28-Tenax II Combo

Aerial Tessar for Zeiss Ikon Tenax II camera

Zeiss Ikon Tenax II with Aerial Tessar

I have mentioned the use of the Tenax II by the German Navy (Kriegsmarine) in previous Blog entries. Here is a f2.8 4cm Tessar for the Tenax II converted for use in aerial photography. Its serial number (Nr.2383250) is a little over halfway through the last batch of this lens that Carl Zeiss made. The startup date for that batch (11 June 1938) would indicate a manufacture sometime in the fall or winter of 1938-39.

The optical unit has been taken apart and the diaphragm removed, leaving the lens wide open at f2.8. The focusing mount has been removed and replaced with a solid, black-painted block that just holds the lens and its bayonet release. It has no arm for the rotating wedges so there is no rangefinder. The lens is coated, unlike earlier Tenax II lenses for the civilian market. A yellow filter is permanently mounted on the rear of the lens.

At one time a stop was screwed to the outer flange that would have limited the shutter speeds to the top two: 1/400th and 1/200th of a second.

An inventory number, “MF728” was hand engraved and white-filled on the back of the lens.

'M' stands for 'Marine.' There is no consensus as to what the F stands for.

All these modifications makes a so-equipped Tenax into an easy to handle, point-and-shoot camera for pilots who were also photographic tyros. The plunger advance would have made it easy for a pilot to snap off two or three shots in rapid succession even while controlling an aircraft.

But why use the maximum aperture? If figuring a film speed of around ISO 50 by modern rating, bright sunlight with the filter factor figured in would have given an exposure of f2.8 at 1/400th of a second—exactly what this combination was designed for.

The Tessar disassembled.  Note the opening under the brass sleeve that would have been the access for a diaphragm control. Also note the number scratched into the brass. To the right is the yellow filter that mounts on the back of the lens.