Birefringence basics

In one of my previous posts I mentioned birefringence. Here are some more details.

Polarizers set up the direction of light polarization. If you apply two filters at the same time you can get  complete light blocking, complete transparency or something in between. This is how some adjustable Neural Density filters work. 

Some materials change the polarization of the light. If such object is place between two polarizing filters set to maximum blocking, the only thing one can get in the picture is the light disturbed by such material.

In order to try birefringence photography following are needed:
source of polarized light  - LCD screen/tv/monitor/tablet works perfectly. 
object made of material that disturbs polarization - cheap plastic is perfect, hi-quality glass is useless.
polarizing filter attached to your camera.

Place object in front of the polarized light source, rotate the filter so the source looks black and shoot.

Depending on orientation of the object polarization changes, so try moving object around.

As example I used plastic bag/pocket. First two pictures are without setting the polarizing filter to full black to show how the orientation affects color.





And now with polarizing set up to black



The thicker material the more interesting patterns you can see. 

The color of the light (or image displayed on the screen) affects the result. First I used blue droplets background (filter not set to full black).



Now with filter set to black:



The same setup, but with green/yellow background displayed on the screen:



The more complex shapes add more patterns to the polarization and in effect more interesting result





Hope you will enjoy your birefringence project. Please add comments or questions. I'm feeling quite alone in this blog ;).

Hair birefringence and LCD backlight

One of the tricks I tried is birefringence of plastic objects. I set up LCD screen (tv), polarizing lens and some objects that would generate required effect (like the bottle below).



At some point my daughter walked into frame. She usually moves way to fast and considers posing to be extremely boring. This time she was preoccupied with some snack and I managed to shoot few pictures. However it was done with the setup I had for testing birefringence (in front of LCD TV, and my lens had polarizing filter on). I immediately discovered that her hair affected light in similar way as some plastic objects.



From this came idea of using LCD screen to highlight the hair of the person. Few days later I shoot few more pictures with slightly better light setup,



I tried it with myself as subject, but since my hairstyle is far from lush/luxuriant the effect was not that great. It doesn't mean it was complete disaster. Hair were highlighted from the back with the colors displayed on the screen.



This led to more attempts and LCD displaying color patterns can create interesting lighting for portraits. I didn't use much of the additional lighting (just whatever was available in the room), however to add some dramatic lighting I held a tablet with a one-color image displayed. Below is the test with some pattern displayed on screen (I have intentionally rotated polarizing filter to show the pattern behind).



Tools needed:

• Lens with polarizing filter.
• LCD TV (the bigger the better).
• Ability to display patterns on that screen.

Process:

• Put subject in front of the screen (back toward screen).
• Display color or pattern on the screen.
• Rotate filter so the screen looks black.
• Shoot.

Tips and Tricks:

• Distinct patterns (like horizontal b/w stripes) do not have much effect. I was hoping that skin would reflect part of the pattern, but was unable to do so. I will try to make skin more reflective by using baby oil in the future.
• Color wheels, or two color gradients work nicely.
• If subject is close to the screen the effect of back-lighting is more visible.
• Clean your screen - the dirt on the screen (yes - I'm ashamed) is adding bright spots to the background - I had to remove it in post-processing. As example see last picture.

Hope you enjoyed it and will have some fun testing this technique. I would appreciate any comments/questions/suggestions. I will answer them as fast as I can.