Archived posting to the Leica Users Group, 1998/05/02

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Subject: [Leica] "Normal" perspective
From: Dan Cardish <>
Date: Sat, 02 May 1998 15:46:04 -0400

At the risk of beating a dead horse, I have a formula for determining the
enlargement required for a given image to appear to have normal
perspective.  This formula will work for any focal lenght lens.

Let:  vd= viewing distance
        fl=focal length

Then normal perspecive occurs with an image magnification of

m = vd/fl

For example, with a 50 mm lens, a photograph viewed at a distance of 10
inches (250mm) will require a magnification factor of 5 to appear "normal",
meaning that when viewing such a print, at that distance, the image on the
print can be superimposed onto the original scene with perfect
registration.  If you were viewing the print in a gallery where viewing
distances are greater, a larger magification will be required to achieve
the same "naturalness", otherwise objects in the photograph will appear
smaller than normal (a wideangle look).  

Dan C.