Ed, Super images. I line 10 and 15. The camera is exceptional. And the lens is genuinely great. It is a Tessar type. Argus drawings (courtesy Phil Sterritt) show that the back group uses glass that is a thorium oxide blend. This allows the lens to hold up all the way to f/2.8, vs. the usual Tessar limit of f/3.5. I think some old Industar lenses found on FED and Zorki cameras use the same, as well as a number of Kodak, Pentax and Canon lenses. And some of the Voightlander Lanthars used lanthium rather than thorium, but with similar advantages. Mike
