It's also worth bearing in mind that the transmission of lenses improved very significantly with the advent of coatings in 1938 although it was after WWII when coating s became universal on all quality lenses.

The first coated lenses from Zeiss have a red "T" designation for Transparent, earliest I've seen was a 1938 CJZ 15cm f4.5 Tessar, I have an early 1950's version and the coatings are excellent althogh a touch blue for colour work.

Before coating was commom many photographers processed to higher negative contrasts to help overcome slight lens flare, by the early 1960's this had changed and the ASA/BS testing of films was revised resulting in nominal film speeds being doubled (Tri-X went from 200 ASA to 400ASA).

Ian