Polarized electronic flash...Part 1

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twebster
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Location: Phoenix "Valley of the Sun", Arizona, USA

Polarized electronic flash...Part 1

Post by twebster »

Hi y'all :D

It's going to take me a while to put together an article on polarized flash so I thought I would post a quick "how to". I was erroneously calling this method "cross-polarized" flash. I borrowed that term from microscopy when imaging birefringent crystals. Sorry if I created any confusion.

Polarizing filters work by only allowing light waves vibrating in the same direction to pass through the filter. Glare is caused by light waves that vibrate in many directions. By only allowing light rays that vibrate parallel to one and another to pass through the filter glare can be greatly reduced or eliminated. If we illuminate an object with our electronic flash the flash emits light rays vibrating in all directions. Placing a polarizing filter over the flash allows only light rays traveling parallel to each other to leave the flash head.

Why do we, then, need to add a second polarizing filter to the camera lens? Simple reason...after the light from the polarized flash strikes our subject some of that light is scattered and vibrates in different planes. Aligning the polarizing angle of the filter on the camera lens to the same polarizing angle of the filter on the flash eliminates the light vibrating in different planes. This almost eliminates all glare from the subject and also allows colors to become more saturated.

The polarizing angles of the camera filter and the flash filter must be in alignment and parallel. The further off-parallel the less light that can be used for the exposure. Turning 2 polarizing filters so that the polarizing angles are at 90° to each other will basically eliminate all light passing through the filters. Intermediate angles will act as neutral density. To determine if the polarizing angles of 2 filters are aligned simply place one filter over the other and turn one of the filters. When the view through the 2 filters is the brightest then the polarizing angles are aligned. If the view through the 2 filters is completely black then the polarizing angles are 90° to each other and no light can pass through the filters. Here's the first setup I tried...

Image

The flash and the circular polarizer (above) are laying on a sheet of polarizing material I bought from SurpluShed. I cut a small piece of polarizing material the size of the flash tube on the flash head and taped it on the flash. The double arrow indicates the polarizing angle of the filter (see the image below).

Image

I place a circular polarizing filter on the camera lens. Camera polarizing filters come in 2 types: circular polarizing filters and linear polarizing filters. They act the same so I won't go into the differences. If your camera is an autofocus camera you will need to use a circular polarizing filter. If your camera is a manual focus camera you can use the lesser expensive linear polarizing filter. Polarizing filters for photographic use have rotating mounts. You screw the filter on the lens and rotate the filter in the mount to the desired polarizing angle. These filters usually have a reference mark on the filter mount to indicate the polarizing angle (see the image below).

Image

The double arrow indicates the polarizing angle. The single arrow indicates the reference mark. When I use the flash with polarizing filters I just make sure that the polarizing filters are aligned by referring to the reference mark on the circular polarizing filter. This almost completely eliminates all glare from the flash when I shoot images of "macro-critters". Here is my rig (see image below)...

Image

The Kirk Enterprises Macro Flash Bracket holds the flash directly above the camera lens. I have indicated the polarizing angles of both filters with yellow arrows. The red arrow points to the index marking on the camera polarizing filter. As long as the polarizing angles are parallel, glare from the flash will be eliminated.

Now go to Part 2... :D

Best regards to all as always, :D

(Never mind that I have gone over the allotted number of images :shock: :!: )
Tom Webster
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Phoenix "The Valley of the Sun", Arizona, USA

Think about this...maybe Murphy is an optimist!!!

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