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The Poor Man’s Polariser…Got Shades?

I recently introduced you to the concept of polarising microscopy. Naturally, if evaluating refractile material is an everyday part of your research, it is definitely worth investing in a professional polariser modification for your microscope. But if you only use a polariser occasionally, this might not be the best use of your lab’s money.

In a pinch, however, you can try a couple of less costly alternatives.  The “poor man’s polariser” is a term often used to describe the use of anything cheap that will create some of the effects of a polariser. One way involves adding a couple of home-made polarisers to the optical train, one below the specimen and the other above it.

The lenses from polarising sunglasses can produce amazing effects when added to a simple microscope! It’s no coincidence that a professional polariser filter looks like the lens from a pair of sunglasses. They function similarly too.  You can set it up in just a few easy steps:

  • Find an old pair of sunglasses! The cheap, plastic clip-on types that sit over your glasses are ideal for this purpose, especially since they’re easier to cut.
  • Cut a disc from one lens that is big enough to snugly cover the light source at the bottom of the microscope (to serve as the polariser). Place it on top of the light.
  • Cut a second disc that will fit inside the ocular lens (to serve as the analyser). Remove the eyepiece and place it inside so that it lies up against the stop (you can also just place it on top of the eyepiece – use a little plasticine to hold it in place, or even fix it into a cap to place over the eyepiece. The aluminium caps from blood culture bottles work well, and they have a ready-made central hole for viewing. Use the cap’s rubber seal to fix the Polaroid disc in place – cut a similar hole in the seal and replace it in the cap, over the disc. (You could even just place this second disc on top of your slide. Although it causes a lot of blur, it works ok at lower magnifications to simply scan for the presence of refractile material. But the blur does make it less useful if you need to examine your material at higher magnifications.)

Your home-made polariser set-up is now ready, and you use it just like you would use a professional polariser:

  • Before placing a specimen on the stage, look through the ocular and rotate the polariser until the field of view becomes as dark as possible.
  • Now place your refractile specimen on the stage. If you don’t yet have a slide ready for evaluation, a simple piece of cellophane wrapper will do!
  • Rotate the polariser lens to see your new polarising set-up in action. The refractile nature of your specimen will  become evident as you do this.

So now you know how to customise your microscope cheaply to become a polarised microscope. This obviously won’t produce the same results as with professional level polarisers, but if you need to quickly check your specimen for refractile material, this technique can often work well if you don’t have the real thing.

Do you have any old sunglasses lying around that you can put to good use in your lab?  Don’t miss our previous article on other cool lab hacks!

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