Re: Koehler illumination in conoscopic observation

On Nov 28, 3:34 pm, Andy Resnick <andy.resn...@xxxxxxxxxxx> wrote:
Kevin Cunningham wrote:

<snip>



A ground glass filter should be used, I'll bet there is a place for
one. Other wise I'd put it close to the lamp, if possible directly in
front of the lamp. Then, technically, your using critical
illumination, not Kohler but who cares?

I don't think that's correct- critical illumination is the Fourier
transform of Kohler illumination: the filament is focused onto the
sample plane rather than the entrance pupil of the condenser. And
actually- that's the better solution.

Using a ground glass plate is a kludge to destroy the image of the
filament in the back aperture of the objective lens; it may work, but it
isn't critical illumination.

--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University

Dr. Resnick, Good points! I've been having this discussion over a
few years with some buddies in Germany and Austria. I should have
known better. What NoSpam and I were discussing was whats commonly
called either critical or Kohler illumination.

In fact no one uses either exactly. The usual start point is a ground
glass assembly, take a look in the base of a modern microscope there
are between 1 and 3 ground glasses. This is because designers know
that if you use a specially designed lamp with a thick filament they
are a pain to get, expensive and in a few years very few will be
used. Its simpler to use ground glass and a lot cheaper.

Thanks,

Kevin Cunningham
SMS
.

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