Re: Kohler illumination question...

Hello All,

IMO the theoretical physical principles as put forth by Dr. Resnick
have merit, but in the practical world of engineered and marketed
items, there are some deviations from the ideal that arise from other
imperitives. The diffuser in the Zeiss design makes life easier and
there is not going to be much of a compromise between the theoretical
ideal and the actual result achieved. This is what I have found in
experimenting with my equipment while swinging the diffuser in and out
of the light path.

Some manufacturers place a ground glass element at the point where the
light exits the base of the microscope through a fixed aperture. This
design eliminates parts and costs associated with the substage optics
and reduces the price of the instrument. The same makers also make
compromises with the ALL the other optical parts for the same reason.
Some microscope users think, if the illumination subsystem in their
microscopes can be made to conform to the strict pricinples of
Kohler's work, the image in the eyepieces is going to improve
miraculously. That is not likely to happen. They are neglecting, the
critical role of the other components.

An abstract discussion of the merits of one lighting system over
another is stimulating and interesting, but it may not show the way to
any practical advantages or improvements to a given instrument because
so much depends on other elements in the design.

Aaron


On Tue, 03 May 2005 04:21:25 GMT, "GTO" <gregor_o@xxxxxxxxxxxxxxx>
wrote:

>I took a closer look at the technique used for the "diffuser" and I can only
>agree with Aaron and Klaus that the surface structure of this optical
>element is very interesting. Before we can draw any conclusions some serious
>experiments must be performed. Experiments that Zeiss and Leitz have already
>conducted.
>
>Considering the fact that the great optics experts from Zeiss and Leitz came
>up with this subtlety to better implement Köhler illumination (or Koehler,
>if you do not want to use ASCII 148!), I believe that it is worth to more
>carefully study this detail.
>
>In Physics many things can be explained, as long as the Physics can model
>the real world situation. But as in so many cases in microscopy, with our
>current understanding in Physics we cannot explain it all. Of course,
>Physics, as an extremely important tool, guides us, but sometimes it may
>blind us. What I am trying to say is that I could learn all there is from
>countless text books in optics and I would still not be able to build the
>best implementation of a Köhler illumination. Why? All implementations are
>flawed. And, in the flaws we recognize the truth and not in elegant
>equations.
>
>I would not be surprised if we see further improvements even in the design
>of our old Köhler illumination.
>
>Just my two cents ;-)
>
>Gregor
>
>"justbeats" <steve_beats@xxxxxxxxxxx> wrote in message
>news:1115071384.034943.147380@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> Not sure where to step in here - and I'm somewhat daunted to do so
>> amongst such clearly well-informed correspondents. But as the OP who
>> started this thread, may I humbly observe that my original question was
>> prompted by a suspicion that the crtical V kohler thing hid grey areas
>> that hadn't been described or discussed at length in an online forum
>> (to my satisfaction, anyway)
>>
>> It seems I was right in the general sense, and while the discussion is
>> very interesting, any consensus reached will make no difference in
>> practical terms. In summary: as long as the approximate focus of a
>> Kohler/critical illumination system is somewhere between the filament
>> and the ground glass - the final result will always be judged on the
>> subject, not the fidelity of it's reproduction.
>>
>> Cool stuff though! I'm learning a lot - please keep it up :-)
>>
>> Cheers
>> Beats
>>
>

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