Diagonals of common film formats (and the focal length of a Tessar type
lens which will cover that diagonal with minimal fall off --so called
normal lens):
135 43mm
6x6 83mm
6x9 105mm
4x5 165mm
5x7 210mm
8x10 330mm
One will note that old Rolleiflexes came with lenses shorter than that.
Presumably that was because the designers figured that prints would be
cropped square and the fall off in the corners would not matter. The
more expensive Xenotars and Planars did cover the diagonal without
noticable fall off.
Another note is that 50mm was selected for the original Leica because
that was the standard focal length for 35mm motion picture cameras of
the period. And stricty speaking 135 film is double frame 35mm, the
movie film frame being 18mm x 24mm. So your *istD is nearly full frame
<grin>.
graywolf
http://www.graywolfphoto.com
http://webpages.charter.net/graywolf
"Idiot Proof" <==> "Expert Proof"
-----------------------------------
William Robb wrote:
----- Original Message ----- From: "Gautam Sarup" Subject: Re: crop
factor vs. telephoto factor
Adam,
Using the diagonal as the standard one would expect the
normal for a 8x10 frame to be about 325mm while the practical
standard as you mentioned is only 210mm. That's approx.
only 65% of the diagonal.
Do you know where the large difference comes from?
Adam mixed his formats up. A 210mm is closer to standard on a 5x7.
William Robb
