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Date: | Fri, 28 Nov 2008 10:20:01 +0200 |
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I am confused with regard to the front focal length of objectives. I thought
that the magnification of an infinity corrected objective will be the distance
between the tube lens and the intermediate image, divided by the front focal
length of the objective (which is where I expect the object to be). Since the
objective is not really a thin lens, I can understand that the actual working
distance may be less than the focal length, since the focal length may need to
be measured from inside the objective casing.
However, I have a paper that describes a 25x/NA=0.5 air objective, which has an
11mm working distance, as having a 25.1mm focal length, while the distance from
the tube lens to the intermediate image is 245mm. This has me confused, and I
realize that I do not understand something fundamental here.
So, I turn to the optics gurus on the list to clear this up, with many thanks in
advance.
--aryeh
--
Aryeh Weiss
School of Engineering
Bar Ilan University
Ramat Gan 52900 Israel
Ph: 972-3-5317638
FAX: 972-3-7384050
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