I found and adapted a previously unknown (in that focal length) ultra wide angle large format lens, obviously a Hypergon design, which Emil von Höegh invented around 1900 for the GOERZ company [he also invented the famous DAGOR lens for them] which was later taken over by ZEISS. Based on that Hypergon design, Robert Richter later in 1934 developed the famous TOPOGON lens for ZEISS, which became the classic aerial imaging lens for quite some time. The earlier Hypergon I have here was made approx. 1950 I would guess with a diagonal angle of view of about 120° (on its designed format of about 145mm image circle).
It turned out that it seems to be a quite useful lens for VIS and UV on my UV sensitive cameras, although it has quite some focus shift in UV (expected from that simple design). The focal length is an estimate, it is somewhere between 24 - 26mm from my measurements. I show the lens aberrations in the following screenshot (scaled to fit that smaller sensor, hence smaller used image angle and object at infinity; for an f11 aperture, which is the optimum for that lens):
Here is a technical article of my friend Marco Cavina, that covers such ultra wide angles nicely with lots of images and diagrams as well as showing never finished prototypes.
Now some photographic results.... [click on image to see a larger one]
[note: measured at f11]
These were also shot using it:
and despite the well known aberrations, using it results in quite useful images, also for visible light photography, thanks to its good contrast and sharpness:
and its good flare resistance:
Quite a nice find I'd say...
Stay tuned, more will follow on that fascinating subject...
More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos