Originally Posted by VAV
Thanks for the response JJJPHoto.. I didn't know 43mm is the diagonal of the 35mm film. But isn't 50mm usually considered to be the 'normal perspective' of our vision?
50mm is used as a standard because it was cheaper to produce a high quality lens with minimal distortion "back in the day" if it was 50mm rather than just a little wider at 43mm.
The idea that 50mm is the normal perspective of the human eye is just an urban legend/myth that has been debunked many times in print, online, and even on TV. The actual normal perspective for the human eye is technically MUCH wider ... as in extreme wide angle ... but our brains interpret perspective in relative terms (which is why sometimes you focus on tiny details like a macro lens and sometimes you look at a huge landscape like a 8mm lens with almost no distortion.
http://www.assassinationscience.com/...0of%20view.pdf
In any case, "true normal" perspective in photography is based on the diagonal measure of the film plane or image sensor ... which is why 80mm is the standard for medium format film.
It has nothing to do with what the human eye sees ... but rather the math involved with calculating the ideal perspective for the imaging surface.