Archived posting to the Leica Users Group, 1999/12/01
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At 11:03 PM 11/30/1999 -0800, Jacques Bilinski wrote:
>" By the "same magnification" I assume you mean the same
>magnification in the plane of sharpest focus. Say the 50mm is acceptably
>sharp X feet closer than the plane of sharpest focus, and Y feet beyond the
>plane of acceptable focus. The 100 mm would not have the same magnification
>as the 50mm at these 2 distances, so it does seem reasonable to me that
>maybe what matters is some king of 'range in magnification' rather than
>simply a set distance in front and behind the plane of sharpest focus.
No, by magnification, what I mean is that a 50mm showing the subject at the
plane of focus of 1/2 life size is going to be X inches from the subject. A
100mm macro lens at 1/2 life size is going to be 2X the distance. At the
same aperture, the depth of field will be exactly the same between the two
lenses. I have talked to many folks who know a lot more about optics than I
that confirm this fact. To say that it is an approximation shows a lack of
understanding of the nature of optics. Of course, focal length varies
between two lenses, but not by that much.
Eric Welch
Carlsbad, CA
http://www.neteze.com/ewelch
"There is nothing so stupid as an educated man, if you get off the thing
that he was educated in. "
--Will Rogers