I recall several photo magazine treatments of his book "The Americans" usually including photographs. These articles were timed to the reissuance of his book. I'm sure there's lots of stuff out there. I remember reading that he used Plus-x film (Tri-x was not yet available). he probably used a pre M Leica screwmount (the M3 not yet available). Some of his photographs seem to be taken with a 50 mm lens others look slightly wider. since the 28mm leica lens at the time was really slow (like f6.3 or 6.8 or something) I'd surmise he used a 35mm lens, as well, or exclusively. his pictures have very little shadow detail, so he must have been stingy with exposure and generous with development.

I'm sure you could look at the Leica Users Group (LUG), Leica Historical Society of America (LHSA) ((favorite leica joke "Join the LHSA, at least you'll never have to look for a doctor.")), etc., to find out what lenses were used in the early '50s.

I read that "the Americans" was very unappreciated when it was published. Popular Photography evidently published a scathing review. Frank's photographs more than withstand the test of time, though I admit that by the time I saw it, I was already exposed to the civil rights and Vietnam war photographs of the '60s, so it had less impact on me, taken out of its histoical context. All in all, a groundbreaking collection of photographs.

I understand that Frank moved more towards movies after "the Amercians".