Cross Polarization or Birefringence

Posted on October 27, 2012

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You knew I was going to write about Birefringence or Cross Polarization sooner or later because as photographers, we all play with this at least once. Does it yield anything good? Maybe. So what is this? Birefringe of fork

A polarizer is often used to take reflections off of water and windows when photographing in harsh light. It can be used to increase contrast (and making a sky more blue, too, in the process). This is how you will use a polarizer most of the time, but there will be times when you shoot with polarized light sources and your camera being polarized, too.

Cross polarization is something that happens when you polarize the light sources and you also polarize the capture device. In this situation, often the light source is polarized in the vertical direction and the capture device, a camera, is polarized in the horizontal direction. Key to this technique is that you always have the camera polarized 90 degrees from the light source. You will find this technique useful for a few things when you do table top photography-such as plants, insects, reptiles that are wet, minerals, and artwork. I use this most when photographing artwork for insurance reasons – no need to remove the art work from the frame (there is more than this, I might add, but this is part of it). There are other reasons to do this when photographing an object. Play with this technique with some things and see how it differs.Birifringe of knife

When you photograph something plastic, you get some really interesting colors and patterns. That reactions is called Birefringence and it shows the stress within the clear plastic object you are photographing. Examples of this are on this post.

To take these images, start with finding some really cheap clear plastic items. The cheaper they are, the better. Glass won’t work. Dollar stores are the best places to start your search. Craft stores are your next. And, don’t discount other clear plastic items. Try as many items as you can find. Plastic silverware, glasses, plastic wrap, Christmas ornaments, plastic packaging, etc. The key to to find as much as you are able to before you do the shoot.

Next, you have to make sure you have a polarizer for your camera and that you get some sort of polarized light source. You can convert any light source into a polarized source with sheets from Polarization.com. This is the least expensive place that I have found that produces a quality product. You can expect to pay somewhere between $15-80/square foot for polarized film sheets, depending on the place you get them and the manufacturer. You say “wait a minute! There has to be a cheaper way!”. And there is. If you have an LCD display (or laptop) or TV, and you can get a perfect white tone on it (set it to full brightness), you can use it. LCD Displays utilize a form of polarization to adjust brightness on them – so it is key to have them display white and be at full brightness.Birifringe of fork 2

I should mention if you have autofocus, you will need to get a circular polarizer or the autofocus might not work with linear polarizers. If you want to focus manually, feel free to use any type of polarizer.

[update: I have had many people comment that you need a macro lens – either a 100 or 85 mm prime lens. The images shown here were taken with a 70-200 f2.8 lens. One image was taken with 55-200 f4.5-5.6 with a one diopter filter attached – it is the one of the fork where you can see the vertical lines of the LCD display and the blacks don’t quite show up as black.]

Now we are ready to set everything up. Set the light polarized source flat on the ground. Set the plastic item on the light source. Make sure you have a polarizer on your lens. Then adjust the polarizer on the lens until the white turns dark. You should then see the colors on the plastic item appear the brightest when you do this.

Finally, start shooting away.

Birifringe of CDROM coverBirifringe of Tiffen filter holder.[Note: There is no endorsement by or from Tiffen for this blog or its posts. The filter holder just happens to be one of the objects I found that was clear plastic that I chose to shoot for this blog. Tiffen is a registered trademark and service mark for Tiffen Company. XOIND Studios and Don Krajewski neither endorses or discourages use of Tiffen products.]

Birifringe of vacuum formed plastic

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