Visualizing the effect of a microscope's condenser aperture

[rjlittlefield]

From time to time, somebody asks if there's an easy way to visualize what a microscope's condenser aperture does to the light beam.

For not much money, one can buy an elegant device that is specifically designed to do this job.

Or, for a quick demo using stuff that you might already have lying around, you can use a very dilute solution of milk in a small plastic container.

The colloidal fat does an excellent job of scattering just enough light to see what's going on. Just don't use too much -- a couple of drops in a half-cup of water is a good place to start.

Be sure also to use a flat-bottomed container.

The illustration shown here is using the NA 1.2 condenser from an aus Jena Laboval 2 microscope.

The top row is with the plastic container "oiled" to the condenser using water. The bottom row is using the condenser dry, at maximum aperture, and demonstrates the narrower maximum cone imposed by using the condenser dry.

--Rik

[Ken Ramos]

You know this is one of those things I have often wondered about, "how it works" but have never bothered to ask. Good demonstration there Rik.

[rjlittlefield]

Thanks, Ken.

BTW, in using this technique it's important that the milk be extremely dilute. If you put in too much milk, you "fuzz out" the path of the beam. The stuff I used in the photos above is about as dense as you can go and still get a good impression. For more careful work, you want a solution that you can see clearly through, with just the slightest "milkiness" to scatter a small amount of the beam sideways so you can see it.

Here is an oblique view that shows what I mean. Notice that the microscope stage and condenser parts are still clearly seen through the dilute milk, which is about 1 inch thick in this setup.



The device I mentioned earlier uses a different mechanism -- it fluoresces rather than scatters. That allows a much brighter image of the beam without disturbing its path. Far superior if you need to give demos on a regular basis, or in a normally lighted room.

--Rik

[Ken Ramos]

The fancy green gadget has its purpose as far as being handy for demonstration but it seems your "homemade" device clearly shows more of the physical aspects (in 3D) of the beam of light itself passing from the condenser to the objectives. It may require a dark room but it is a much more informative means of demonstration or at least I would say so, especially in that last or second image you've shown.

[Smokedaddy]

For not much money, one can buy an elegant device that is specifically designed to do this job.

--Rik

Out of curiosity what is the elegant device since the link is broken?

-JW:

[rjlittlefield]

It was a cylinder made of fluorescent glass. In operation, glass inside the cylinder would glow green wherever it was touched by bright light from the condenser. Because the mechanism was fluorescence rather than scattering, there was no blurring or "fuzzing out" of the condenser beam.

The text of the missing page can be retrieved from the Internet Archive, currently at https://web.archive.org/web/20081121130 ... linder.htm . Unfortunately the images were not archived, and I cannot find them anywhere else.

--Rik

[Smokedaddy]

Thanks ...