Thursday, 13 February 2020

Using Crossed Polarising Filters on a Conventional Microscope

A short while ago I posted an article about sugar crystals imaged in a microscope with crossed polarising filters. I promised to show the setup I used to achieve this, so here we are.


What you see here is a Charles Baker microscope with a Cooke microscope lamp providing Köhler Illumination. (The link is to my previous article explaining Köhler Illumination). I've implemented the crossed polarisation very simply.

I have a small polarising sheet that I have cut into two two-inch squares.
I use one of the squares in a filter slot in the microscope light.
And I place the other over the microscope slide, but under the objective lens. This sheet of polarising filter I rotate, while viewing through the microscope, until I see the best contrast.
And the result... I get to see these wonderfully colourful renditions of the crystalline structure of the sugar (see my earlier post).


A microscope used with crossed polarising filters is sometimes referred to as a polariscope.

Polariscope

In general, a polariscope is an optical inspection device used to detect internal stresses in glass and other transparent materials such as plastics, synthetic resins, crystalline materials, etc. A polariscope is composed chiefly of a light source and two crossed polarised lenses. Material to be examined is placed between the two polariscope lenses and viewed through the lens opposite the light source lens. It is commonly used in detecting the optical properties of gemstones.

All content and images © Tony Benson


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