Zeiss Planitar 180mm f/4.5 ???

Just when I was thnking I kenew lenses semi-well, a weird one comes along...

Zeiss Planitar 180mm f/4.5, you can see an example here:

http://www.macrolenses.de/ml_detail.php?ObjektiveNr=161

The very few other references I can find only reveal it is a "1:1 repro lens". But the above link refers to it as a "Reflective Repro Mirror Lens", and it has a seemingly unremoveable front lens cap with a mirrored inside surface (seen through the rear of the lens). I've tried unscrewing and prying, but it won't come off, and appears to be designed not to come off.

Any insights on this before I start tearing it apart? It's just a $20 impulse buy, but I'd like to understand just what it is before I do something irreversible...

It's from an older copier machine and thanks for quoting my site;) I also have that one sitting around unused...