Recently I've came across very unusual lens - Leitz Epar 600mm f/4.5. The lens has fixed iris (a little bit smaller than internal body diameter), also it seems that front and rear elements are cemented doublets and there is another glass with a little (if not flat) curvature in the middle. No signs of coating at all. Body of the lens consists of two parts - internal (which holds all the glass) made of chromed brass and outer made of brass and black painted. There is some kind of focusing mechanism (like one used in projector lenses).

Unfortunately I can't find any information about this giant beast (and it's really huge one!). Can you tell me any information about the lens?

Thanks!