"Gary Morrison" <mr88cet@austin.rr.com> wrote in message
news:3F3B8626.FFB197F@austin.rr.com...
> > the "normal" or standard lens is usually a fixed focal lenght of 50mm.
>
> For 35mm, yes, but what about for any arbitrary given film or CCD size?
Or
> how about 70mm movie film, or 35mm anamorphic prints of movies?
>
> One reasonable reply directly to me suggested that its based upon the
viewing
> angular distance being about the same as the human eye, and said that this
> number works out to around 48-55 degrees.  That seems plausible, but it
> doesn't say anything about width vs. height.  I'm not sure how to relate
that
> rule to formats like 70mm wide-screen, or IMAX, wherein a normal lens is
> carefully designed to provide not only a normal view in the center area of
the
> screen, but also a lot of peripheral-vision image content.  If you project
> IMAX onto a typical TV screen for example, it looks very wide-angle.
>
> It seems likely then that the formulation has to include a component of
how
> far away you are from the print or projection in viewing the image.
>
>
Sorry bud you lost me right after "For 35mm, yes", LOL
Ok lets try this then,
Ansel Adams defines a "Normal" lens as "one whose focal lenght is about
equal to the diagonal of the film format. Such a lens will have an angle of
view of about 50 degrees to 55 degrees, comparable to what we consider
normal human vision. A 50mm  (2-inch) lens is considered normal for 35mm
cameras (although the actual film diagonal is about 42mm); 80mm is normal
for 2 1/4 x2 1/14 format; and 150mm to 165mm is normal for 4x5."

From his book The Camera.

Brian.................