Re: Kohler illumination question...

Aaron wrote:

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.

I think you may have been missing the point of my posts, which is simply that a careful analysis of critical illumination and Koehler illumination shows that they are identical in several important aspects. Additionally, it can be shown that when not using either critical or Koehler illumination, the optical system is not performing optimally, and that the diffuser element is generally superfluous. These are not abstract points.

The abstraction comes into play because it is required to provide a precise, measurable definition of "image quality", something that surely varies from user to user.

The question of "reduction to practice" is extremely important, but theory will guide the design. Theory is used to analyze a real system, otherwise the lens designer is simply wasting time guessing about what may or may not be an improvement. If I can understand the underlying theory, I can perform rational trade-offs in the design of real things,using real materials, the properties and characteristics of which are neccessarily more complex than what appears in a simplified (and useful) theory. For example, balancing defocus against spherical aberration.

As for me, the end user, I need to be able to apply theoretical principles in order to (1) understand the marketing hype and (2) know when spurious claims about the performance of an instrument are made.
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
.

Relevant Pages

  • Re: Data modeling in MV, revisited
    ... Whilst many people may have made design ... Yes, but not likely a "best practice," right? ... dictionaries - where EVERYTHING was embodied in code. ... If you start with the business problem, you will rarely end up with the ...
    (comp.databases.pick)
  • Re: Meganet strikes back
    ... > key streams have in fact been used in practice. ... >> Note that aids are killing a whole continent (Africa)! ... your phrase 'access to relevant information' also ... > informed evaluation and verification of the design and ...
    (sci.crypt)
  • Re: Comparing Dictionaries
    ... Though in my daily job I have some coding tasks, I do not see my self as a programmer since in my perspective a programmer is someone who can write good code regardless of the language. ... A functional design is written on the base of the assignment and the scope definition. ... Still there are tons of reasons why you shouldn't follow blindly the best practice, since best practice is founded on theory molded around the most occurring reality. ...
    (comp.lang.python)
  • Trader Alert --- BKHM
    ... Bookham, Inc. engages in the design, manufacture, and marketing of optical ... components, modules, and subsystems that generate, detect, amplify, combine, ... manufacturing industries. ...
    (misc.invest.stocks)
  • Re: Comparing lists
    ... > design of my programs when no computer happens ... hard way), the distance between theory and practice, in practice, is ... >> love big-O because it's easy to compute, ... > acquired, by way of conditioning experiences, ...
    (comp.lang.python)