Steinheil Munchen Macro-Quinar f/2.8, 100mm Find! (w/ one problem)

I just found this lens while cleaning up my parent's house. I tried to research it online, but there is not much about this. The only thing I could find was eBay listings which have this selling for around $500. Why is this such a special lens? What is the history behind this?

I know it is an Exakta mount.

There is a problem with it though. The aperture blade seems to be stuck at almost wide open. I can turn it a tiny bit and it may click a bit and move half a stop, but overall it is stuck.

This is PURELY hypothetical, but I think that 100 mm f/2.8 was a big deal back in the early sixties and moreover - this lens has a macro photography function, which is yet another reason to make the client pay more. FWIW, their 35 and 55 mm lenses were also macro capable and also highly spoken of.

AGX will surely have more info regarding this piece, since the lens is German.

There was also a 135/2.8. I had one, loved the working distance it gave me, didn't like the image quality, which was worse than my 55/3.5 MicroNIkkor's. I replaced my Steinheil with a 105/4 MicroNikkor as soon as the MicroNikkor went on sale.

Steinheil's macro lenses were among the first to market. IIRC, the shorter ones went to 1:1 on their own mounts. Well regarded back then -- a friend got many lovely shots with his 55/2.8 -- but not quite as good as more recent macro lenses. Even so, good enough.