I read someplace not too long ago that this lens has a deep red filter in it, making it not very suitable for general photography (as if it would be suitable in any case). But I imagine that some versions may have had this filter, others not, depending on the intended use. I first read about this lens in The Leica and the Leica System, by Theo M. Scheerer. (Umschau Verlag, Frankfurt, 1960) On Page 57, Scheerer wrote:
"Summar f/0.85--not for the amateur:
"Objectives made with a relative aperture or more than f/1 were made by Leitz as early as 1934! An example is the 75mm Summar f/0.85 . . . it is used for a number of special tasks, for instance by Professor Janker, of Bonn, for X-ray screen photography. During the 1936 Olympic games such a lens was used in the projection room of the German postal authorities for the projection of the television image.
"I have held this magic lens in my own hands--but I would not like to take photographs with it no matter how precious it is."
---Neither would I, Theo. A glance at the photos shows that there's no way to see through the camera's viewfinder. The lens blocks the whole thing. Of course, you could use an auxiliary finder in the shoe--but what about the rangefinder? You need a rangefinder with this lens! Or better yet an SLR screen.