using 2 polarizers - adjustable ND?

Dweller · Mar 6, 2006

Would this work?

stack to polarizers together and rotate them against each other to adjust the amount of light that gets through to have an adjustable ND filter.

Alpha · Mar 6, 2006

The stopping would be exponential i would think. Stacking polarizing filters would eliminate light from a lot of angles.

MyCameraEye · Mar 6, 2006

Stacking two polarizers againmst each other is known as Cross Polarization. It's a very cool technique used more often in the UK and you can get some really cool effects from doing this. You will want to use a tripod, and defuse your light. Also you will want to shoot at something that wiull reflect light in various directions. I know this may sound silly but this is an excellent test subject. Take one of those orange plastic pill bottle you get from the pharmacy and light it with some defused light and then do a 5 econd exposure on it with cross polarization, you will get some wild colors and effects. Once you see what colors you're getting in your shot, retake the shot with your WB adjusted for it.

Scott

KMac · Mar 6, 2006

You need to have a regular (linear?) polariser in the front. Two stacked circular polarisers wont work as intended because circular polarisers have a layer on the back that spins the light into all polarisations again before it enters the camera.

The former set up works well as a variable neutral density filter up to a point beyond which it becomes a special effects type of shot. Whole patches of the image turn to wild and abstract colours. Its fun to mess around with.

Hope this helps,
Kevin

DestinDave · Mar 6, 2006

Can you see this range of colors through the viewfinder or is it something that only the film or sensor can see? Does that make sense? Like flare - sometimes I get bad flare on a picture when I know I couldn't see it in the finder when composing a shot.

MyCameraEye · Mar 6, 2006

I should have been more specif. You will need a plastic polarizer and the one on your lens to do this trick. Take a lamp, put it directly beind the semi-clear object you are going to shoot, put the plastic polarizer over the lamp, then you will want to defuse the light by putting some frosted glass or plasic, after that your subject and then your camera with a polarizer on the lens.

Scott