Things you never knew you needed your IPad for...

I'm interested in polarised light photography. It can turn some everyday objects into something colourful and exciting... things like plastic tubes or plastic knives, forks and spoons. What I needed was some polarised film or sheets . A search on Ebay and Amazon confirmed my worst fears. It was going to be expensive. Then I saw an article in a photography magazine: You could use your Ipad , smartphone or computer monitor as a polarising filter. Most screens these days are polarised material (for cutting reflections maybe?). I already have a polarising filter for my DLSR camera  to reduce reflections in water and darken blue skies, so in theory I had everything I needed.

I downloaded a free Lightbox app for my IPad. This just gives you a bright white screen to simulate a lightbox which was used in the old days to view slides and film negatives. I setup the IPad so the screen was vertical and arranged some transparent plastic tubes and containers in front of it. I attached the polarising filter to the camera and adjusted it until cross polarisation with the IPad screen was achieved . At this point the screen looks dark when looking through the camera.

I've described the science in a previous post back in July: The other side of Vitamin C. Anyhow, plastic is one of those substances which responds to polarised light in quite a spectacular way. The transparent plastic tubes were transformed into a kaliedoscope of  bright colours which varied as the tubes were turned.

I added some extension tubes onto my 18-250mm lens to give larger magnifications and sprayed water droplets onto the plastic to create some interesting effects.

Why do we get different colours? Because plastic has the ability to turn the plane of polarization of an incoming beam of light. The degree to which the plane of polarization is turned depends on the color of the light and the stress or characteristic of the material at any given point.

 White light is made up of a whole range of different wavelengths which we perceive as different colours if you see an area tinted yellow, this is due to the fact that blue wavelengths that passed through the subject had their plane of polarization turned so that they are now perpendicular to that of the filter on the camera lens and thus blue is subtracted from the beam. If blue is removed then what we see is made up primarily of red and green and thus we perceive that area as yellow.

If we see a magenta area this means that the polarization direction of green light is now aligned at 90 degrees to the plane of polarization of the filter on the camera. What remains once green has been removed from a white beam is red and blue and this we perceive as magenta.