It's an early "T" lens- the inner coatings are soft, if you do open it up- be very careful. The Sonnar 5cm F1.5 of that SN range use set screws hidden under the aperture ring to hold the namering in place, and a set screw to hold the rear section in.
I look forward to seeing some shots taken with it.
For $55 on Ebay, I picked up a J-11 in Leica mount with a Leitz M-Mount adapter. The German made adapters often fetch that price!
I want to see if the focus mount can house the German Sonnar optics module. I also want to take a look at the internal cam- see if it can be adjusted if need be. Basically- the lens was free with the adapter.
That lens is a either a Zeiss prototype or a custom conversion. Zeiss made a very limited run of Leica mount lenses, I've handled an early 5cm F1.5 of similar construction. I've also seen some custom converted lenses.
Hard to know why it is jammed- but I would get an estimate on the value of the lens.
Someday I need to get my computer manual for the IBM Mark I appraised. The Smithsonian has the computer, but not a manual for it. Mine is Autographed by Amazing Grace herself. She asked "Where the Hell did you get This"... It was library surplus, in 1980. I'm glad to have saved it from the bin.
All this looking at 13.5cm F4 Sonnars in LEICA MOUNT, the J-11 lasted exactly 1 set of test shots before putting a 1937 CZJ 13.5cm F4 Sonnar module into it. Worked perfectly, the Aperture index even lined up to the same spot after getting the shim set correctly. Will post some shots this weekend.
The 13.5cm F4 Sonnar is a beautiful lens, and that black one: is STUNNING!