I have long believed the definition of "standard" focal length to be
based on the diagonal of the film frame. Not knowing where I picked up
this piece of wisdom I searched the net and quite to my surprise what
should I find but the works of our own John Lind on the "Science of
Photography" at: <http://johnlind.tripod.com/science/sciencelens.html>
"The standard or "normal" focal length is one that approximates the
perspective and, to a lesser extent the field of view (not including
peripheral vision), of the human eye. The accepted standards spanning
different sizes of film formats is a focal length approximately the same
as the diagonal of the film plane, or a diagonal angle of view between
50° and 55°. In small format 35mm the 24 X 36mm diagonal is about 43mm.
Lenses with focal lengths between 40mm and 55mm are considered
"normal" with 50mm overwhelmingly the standard length."
Back in the 60's when Japanese fixed lens rangefinders were much more
common than SLR's it's my recollection that your camera was much more
likely to have a lens of about 42mm focal length and thus very close to
the film diagonal. I suspect that the addition of the mirror box forced
lens designers to opt for a longer focal length as standard and some,
such as Minolta, even went to 58mm as standard. I think the 50mm
"standard" is only there to avoid the expense of having to use a
retrofocus design on the lens that comes with every camera. That's just
my speculation but I consider it a reasonable guess to account for what
I think was a transition of what's considered "normal".
I suggested the 21/2 since the diagonal on the E-1's sensor is 21.8mm.
Chuck Norcutt
Moose wrote:
> Chuck Norcutt wrote:
>
>
>>Since the definition of the "standard" lens is focal length equal to the
>>diagonal of the film (43mm) the 21/2 would make for a better fit to the
>>"standard" lens definition if you have one.
>>
>>
>
> I'm not sure I follow that one, Chuck. For those who consider 50mm to be
> "normal" for 35mm. 21mm would definitely be wider on 4/3.
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