Using two Polarizers to make a variable ND

[trentp]

Hey so I am picking up a 7D and am super excited about the depth of field and naturally I plan to use it to get the shallowest depth of field possible, or at least for some stuff. So I know I need some ND filter and I dont know what route to go. The Vari ND looks nice but the $350 price tag doesnt look so nice. I know people are doing it using two polarizers, is this an alright route to go? I am worried about the changes in the color at each variation...

The technique can be seen here:

http://www.digitalphoton.net/making-a-variable-nd-filter-with-circular-polarizers/

 

[Michael Olsen]

I believe the more common setup is a linear polarizer on top of a circular polarizer. It does create the "polarized" effect (which, in my opinion, isn't such a terrible thing) and cuts way down on the shifts in tonality.

 

[ydgmdlu]

I am worried about the changes in the color at each variation...

DIY variable ND using two polarizers is what I use. You won't see color shifts until you get into the extremely dark end. Honestly though, the $350 Singh-Ray and the cheaper Fader ND from Hong Kong work exactly the same way and have exactly the same issues. Both of those commercial products specify a usable ND range, and if you go outside of that range, you will see exactly the same color shifts and "crossbar effect" that you see with a DIY solution.

If you go the DIY route, try to get a circular polarizer with a thin frame (usually advertised as 5mm or 4mm) to avoid vignetting when you stack a linear polarizer on top of it.

 

[SonicStates]

Honestly though, the $350 Singh-Ray and the cheaper Fader ND from Hong Kong work exactly the same way and have exactly the same issues. Both of those commercial products specify a usable ND range, and if you go outside of that range, you will see exactly the same color shifts and "crossbar effect" that you see with a DIY solution.

Are you talking about the 2~8 stops they mention on their Ebay store...or is there something I am missing. I have one of these but haven't tried it out because waiting for adapters is a drag... Would love to hear any extra info.
Cheers,
Sam.

 

[ydgmdlu]

Are you talking about the 2~8 stops they mention on their Ebay store...

That's exactly right. Here's what Singh-Ray has to say about the matter:

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.

 

[ydgmdlu]

Singh-Ray also sells the "Vari-N-Duo," a combination variable ND and polarizer filter. But you can see from the product image that it's just two polarizers stacked on top of each other. It's $390. What a rip-off!

The only thing that it offers over a $90 quality DIY solution is the markers for the stops in its nominal ND range. Is that really worth $300?

 

[trentp]

If you go the DIY route, try to get a circular polarizer with a thin frame (usually advertised as 5mm or 4mm) to avoid vignetting when you stack a linear polarizer on top of it.

So if I do go this route I am assuming I should go for some good polarizers, yeah? And what brands are good? I know tiffen is pretty good, what about hoya, ect..?