These lenses appear on Ebay occasionally without any name, only the words, Lens made in Germany, and the 1:1 engraved on a wide adjustment ring. The 1:1 reproduction ratio is a big giveaway that this lens was optimized for work at 1X. The aperture ring has 1/4 stops, and the range is limited from f/5.6 to only f/16, so the lens was likely designed for copy work. But, the most important detail, the serial number, tells you its a Schneider-Kreuznach lens for sure.
Considering these no-name lenses sell for a bargain price, I payed less than $50 USD, what could go wrong?
When the lens shows up, I couldn't help wonder, why the box was so big and heavy for one lens.
This is a huge lens!
Using the search terms "huge Schneider 1:1 lens", google turns up an old archived Schneider C-Claron copy lens brochure in PDF format.
These are the specs for the lens:
Schneider-Kreuznach Vario-C-Claron copy lens
8 elements in 6 groups
240mm f/5.6 optimized at 1:1
to
255mm f/7.0 optimized at 1:0.61
Image diagonal 450-354mm
Multicoated
Lens production, late 1974.
No lens mounting threads or filter threads.
Since this is a copy lens, the field should be flat, chromatic aberration control should be very good, and vignetting should be almost zero, but this lens was designed to be mounted to a bracket, it doesn't have a lens mount, or even any threads, so it looks like it is going to be sitting on my bookshelf in the future.