In article
, N
writes
If perspective has nothing to do with focal length and only relates to the
distance between the subject and camera, what makes a 50mm lens normal?

Several assumptions; you use it on a 35mm full frame camera, you make a
print from the full frame, you view the print at the same distance as
its diagonal. If you do all three things then the angle between subjects
in the photograph should be the same as in the original scene. It has
noting to do with the angle of view of the human eye, which is either
much less if you only consider the fovea, or much more if you understand
how human vision works. It also has nothing to do with the ease of
manufacturing the lens, otherwise sub-miniature (small sensor) and large
format cameras would all use 50mm lenses. Although the normal for 35mm
full frame should be 43mm, which makes the 'correct' viewing distance
for a frame taken with a 50mm lens 1.15 times the diagonal. Why 50 was
adopted instead of 43 is a question for more research; perhaps marketing
and being able to describe it as a two inch lens, but this is surmise on
my part.

--
Ian G8ILZ
There are always two people in every pictu the photographer and the viewer.
~Ansel Adams