Tardigrades and polarized light (I) |
Microscope box, 1970s, with a rather modest microscope, but with ample accessories: Colorants , embedding media and other chemical helpers, specimens including a dead flie and/or a dead spider and the typical butterfly wing (well, from a dead butterfly, of course. Apparently no-one was too scrupulous in this era). Micro projection screen, porcelain mortar with pestle, beaker glass, foam for microtome cutting, filter paper, a permanent specimen on a slide, pipette, scissors and more. |
When judged with the eyes of the truly scientific scientist all this bonus material might be considered as rubbish or primitive educational toy at best. But we do not fully agree to this verdict, as we are still remembering our own "childish" period when we had a lot of fun with this mixed media rubbish. We have taken out and photographed a few items in order that you will be able to make up your mind, just as you like. |
Some selected items from the microscope box. |
When looking closer on to the image above you will notice many objects
which might be not easily accessible just for a few bucks, even in times of the internet, Ebay etc.
For example petri dishes, loupe, sample container, scalpel, coverglass positioner for the fabrication
of permanent specimens on slides (metal, the object with the square window), a cardbox spacer
for the preparation of dry specimens without embedding medium, microtome embedding wax, a simple hand microtome
(the black cylinder in position 10 o'clock), a metal needle, a glass stirring staff,
test tube with cork, test tube holder, and even "terribly dangerous" chemicals like pure 100% alcohol,
which might be difficult to buy at a local pharmacy nowadays. |
Keeping in mind the tiny tardigrade dimensions we will discuss polarizing filter
addition in the normal compound microscope only, for transmitted light.
In principle, polarized light can be used in the dissecting microscope (under incident light)
as well but we will not include this kind of application here.
There is no need for big financial investments. Basically you will only need
a so-called "polarizer" under the microscope table and a second, identical "analyzer" above
the microscope table.
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Removal of the filter glass from a photographic polarizing filter.
In most old fashioned photographic polarizing filters the glass filter is simply kept in place by a threaded ring
which can be removed by help of a fine screw driver. In some cases a bit of
knocking to the screw-driver head will help to get things going or, alternatively,
scratch or even break the filter glass ...
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Demo experiment to check the polarizing filter equipment. In this example we used a filter foil and a glass polarizing filter. The polarizing foil was placed on a lightbox, the test specimen (a plastic filter box cover) directly above, and the glass polarizing filter on top. When turning the glas filter clockwise- or counterclockwise there will be moments with most vivid colour and deep black illustrating the polarized light effects. |
The same demo experiment as above, shown in top view. Good polarizing foils and glass polarizing filters will reveal rich colours and a clean black when positioned above each other in the "full extinction" angles. |
In case the polarizing filters should reveal a clean, deep black in extinction overlay position they can be considered as suitable for microscope integration. As a starting point, before going on to the tardigrades, we should check our polarizing filters by means of everday objects like the following: |
Test object 1: wrinkled food wrapping film (measuring ca. 20 µm in thickness) as seen under polarized light. One filter was placed in the filter holder below the specimen, the other one in the photographic tube above the specimen. |
Test object 2: two scratches on adhesive tape,
as seen under the microscope in polarized light |
Don't worry, polarized light tardigrade stuff will follow. |
© Text, images and video clips by
Martin Mach (webmaster@baertierchen.de).
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