The Leitz Wetzlar Colorplan 90mm f2.5 is projection lens for 35mm Slide Projectors.
No filter mount, no aperture and no helicoid. It was used in 35mm slide projectors with 42,5mm mount.
It is very similar to the Leitz/Leica Wetzlar Elmarit-R 90 mm f/ 2.8 (http://allphotolenses.com/lenses/item/c_2916.html#prettyPhoto).
There were many versions over the years. The first one (all metal, image 4) has a 46mm mount, all later versions the 42,5mm mount. Over time, the lens was further developed. Later versions have "CF" (for curved field), "P" or "P2" in lettering. Also some later lenses were produced in Portugal, but with lower build quality.
Links to online resources:
Posted by: Andreas Lindemann Date of publication: 08.05.2016