Homemade Variable ND?

[hunterrichards]

I accidentally may have figured out how to make a better and inexpensive solution to hauling around multiple ND filters. How? By stacking polarizers! For some reason stacking two rotating threaded polarizers and twisting one, you can cut down light transmission from about 1 to 10 stops. I just did a quick dirty test as a proof of concept, I didn't notice any IR problems nor terrible color-shift problems (well, the color temperature changes about 2200 degrees but its linear- all you have to do is raise the color temperature to match)

I shot this whole thing at f2.8 with a 180degree shutter at 500asa in hard sunlight around noon. If this ends up working nicely I think I found a solution for outdoor exposure in different conditions.

(all I am doing in this test is rotating the foremost polarizer filter, they are actually not threaded on the lens but are being held in front of it. I shot my hand just to show you I am not changing the stop at all)

Link: http://vimeo.com/1679768



Anyone else have 2 Polarizers laying around who wants to test this idea?

-Hunter

 

[Brent J. Craig]

It's been done. It works. If you can manage the color shift it's cool.

http://www.singh-ray.com/varind.html

 

[Ryan E. Walters]

Great idea / concept. Thanks for posting the footage- I'm looking forward to seeing it in action (It says that there is still 15 minutes before it is up.) My only concern with this is two fold- what if you do want the polarizer effect and need the ND? Would you need to stack three Pola's? Also, if you do need to stack 3 Pola's, what does that do to the image- is there any problems with all that glass in front of the lens?

This idea intrigues me. Thanks for the tip.

 

[hunterrichards]

Thanks for the link. They are a bit pricey (the real VariND's)- right now with the cheap filters I have this costs less than $100. And with better quality Polarizers, I think the cost would still be less than that.

 

[hunterrichards]

Ok the footage is now up!

 

[hunterrichards]

found this about the VariND's:

"The Vari-ND is capable of densities of more than 8 stops. Results at these densities, however, may be unpredictable. Depending on the properties of your camera's sensor or film, using the filter at its most extreme densities may produce a noticeable "crossbar" effect or slight color shifts. For best results, always use the filter within its nominal range of 2 to 8 exposure stops."

I'm guessing that it means there arent major color shifts when staying within the limit.

 

[Karl Roeder]

Rosco View

Rosco View

Rosco View system does this:

http://www.rosco.com/uk/video/roscoview.asp