At 11:31 AM 1/16/98 -0600, Ken Norton wrote:
>Oops, do we have a magnification ratio calculation error here?
>
>>> I then used a 50mm f/1.4 reversed onto a 135mm f/3.5. This gives roughly
>>> 2.7 times magnification (50/135).
>
>Hmm. Doesn't it go the other way? 50/135=.37 That's 1/3 magnification
>not 2.7x. If I put a 50mm reversed on a 50mm, I get 1:1 magnification. If
>I put the 50mm on a 100mm I get a 1:2 magnification. A 50 on a 200 would
>give you 1:4 magnification. You will only get greater than life size by
>reversing a longer focal length on a shorter focal length. For example, a
>50mm reversed on a 35mm is 50/35=1.4x magnification. A 200mm reversed on a
>50mm will give you 4x magnification (and serious vigneting too).
>
The magnification is defined by:
M=Image Distance/Subject Distance.
Since your image is formed on the film in your camera, the image distance
is the focal length of the lens ("prime" called by John Shaw) directly
attached to the camera and the subject distance is the focal length of the
reversed lens.
Therefore,
M= Focal Length of the prime lens/ Focal length of reversed lens
The top example: 50mm reversed onto 135mm
M=135mm/50mm=2.7
Tomoko Yamamoto
Photographer, Composer, Soprano
mailto:tomokoy@xxxxxxxxx
http://www.charm.net/~tomokoy/
-All the photos (except panorama) with OM's-
http://ep.com/ep/csp.html?csp=1130
-Olympus Equipment Classifieds-
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