My own Leica IIIa is 90+ years old, but the 1930s was the birth of modern film cameras, better emulsions like Ilfor Fine Grain Panchromatic, and Hypersensitive Panchromatic, now FP4 and HP5 Plus, and just as important was a radical change in exosure and processing technique.
The introduction and improvements of the Leica cameras, followed by the Contax, and later the Exacta SLR, also co-incided with the introduction of small, accurate, portable, light meters. The book that embodies the new approach that we still use today is Hans Windsich's "Die Neue Foto schule", published inthe mid 1930s, luckily also published in English as "The New Photo School", revised and updated in the 1950s as "The Manual of Modern Photography - The Technique"
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When we look at or use older cameras and lenses it is important to remember many are still capabe of being used to produce high quality results.
Ian