The diagonal of a 24X36 mm frame is 43.2666mm not 50mm. The Pythagorean Theorem states that the diagonal is equal to the square root of the sum of the squares of the two sides. (Pythagoras 569-500 BC).
Ansel Adams (aka God) says, "A "normal" lens is defined as one whose focal lens is about equal to the diagonal of the film format. ... A 50mm (2-inch) lens is considered normal for 35mm cameras (although the actual diagonal is about 42mm)" (page 53 The Camera)
Al Loeb
I read in the past that some photographers have argued that the 35mm lens is actually closer to being the "normal" lens. Not sure of the math on that though. The difference from 35mm to 42 (43)mm is so similar to that difference from 50mm to 42mm( 43). Seems pretty close math wise.
Ken Weissblum photo imaging: nudes & landscapes www.metaphotography.com
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