THE WONDERFUL WORLD OF POLARISATION – John Duckmanton

Picture3For this you will need 2 polarising filters, a good white light source, camera and tripod of course and a small sheet of very clean glass that can be held vertically between the camera and the light source.

All computer monitor screens are polarised and can be used as your light source. It helps to select a blank, white page such as a document page and turn up the brilliance on the monitor. For most of my illustrations here I used a sheet of polarising paper between the camera and an old enlarger as the light source but you can use a slide projector lamp.

Set up the camera and light source opposite each other so that the light can shine directly into the camera.

Switch the light on and look through the camera viewfinder. You should be able to rotate the filter on the camera until the field of view almost blacks out. Dark blue is OK.

Picture2To test the system, place a clear plastic ruler in the light path and twist it slightly whilst viewing through the camera. You should see all the colours of the rainbow at stress points. Photograph this if you like but it will be hard to keep still. I usually use a macro lens but most modern zooms get very close.

I would suggest using the aperture setting if you can at wide open (f3.5-f5.6) and maybe moving the light source as close to the subject as possible to fill the field of view – any vignetting can be cropped out on the computer.

So far so good. Now for the glass. A piece 6×4 from a small photo frame is big enough, in fact you can buy a wooden frame in Blackwood for around $2.50 at the discount shop. Take the glass out and clean it then staple/glue/pin a piece of card to the bottom of the frame to give you a vertical holder for the glass! Next you need some cheap cellotape, the yellower the better as the more expensive white stuff doesn’t work (try the cheap shop again).

Place 7 or 8 strips of tape on the glass, criss-crossing, vertical etc and then put this between the polarisers. You should get the effect shown in my example. Slight twisting of the polariser on camera should give a kaleidoscope of ever-changing colours. Photograph away, but if it has worked, don’t demonstrate it to young children as you may never get your camera back!

Picture5If all has gone well, try putting a bit of wrinkled gladwrap over the cellotape, or a clear plastic lid – anything clear and plastic should give you a unique picture.

If you are flushed with success you might want to go on to try some crystals.

Dissolve some pure urea or other soluble garden fertiliser in a little warm water. A teaspoon of each is enough. Spread it out over a small sheet of glass or Perspex and allow to dry undisturbed until it crystallises out. Put between the polarisers again and photograph away. Epsom salts are another good product for this.

The ultimate crystal experience is to use a microscope but this is getting very specialised. Try melting some Flowers of Sulphur onto a microscope slide and allowing it to crystallise out again. One polariser on the light source is often enough to get a good effect, but again experiment.

Better to melt the sulphur outside unless you have a dog to blame for the smell!

 

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