Comments on: Create Your Own Variable Neutral Density Filter

By: aaanouel

aaanouel — Mon, 13 Feb 2012 12:59:50 +0000

“This may be an ok idea for someone who already owns 2 polarizing filters.”
That’s the idea, of course.

“Either way, they will end up purchasing 2 filters.”
Nop!. It works so good that there’s no need to buy a variable ND, they works just the same.

By: Marcy

Marcy — Mon, 13 Feb 2012 04:36:07 +0000

This may be an ok idea for someone who already owns 2 polarizing filters. But for a new buyer, it’s dumb. They can buy a CPL and LP to ‘fake it’, or buy a CPL and VND which will do exactly what they need properly. Either way, they will end up purchasing 2 filters.

By: aaanouel

aaanouel — Sun, 06 Nov 2011 23:10:15 +0000

It also happened to me, I even thought one of the wasn’t polarized… ha!, until I permuted and flipped each of them until getting the right combination.
Once you got it, disassemble filter rings with a scissor and place glasses in the right position in place again and re-assemble rings, finally stack them together.
It will work.

By: aaanouel

aaanouel — Sun, 06 Nov 2011 22:59:40 +0000

There are four ways to combine two CPLs. You have to permute inside faces and outside faces, one on the front or the other. Depending on the combination you get a different effect: one of them is a blue coloration, other is yellow. Just test all combinations, rotate them 90 degrees and one of them will work: when rotating they will go from light grey to totally black.

By: lee

lee — Sun, 06 Nov 2011 20:47:50 +0000

I tried your method out but got a very strong blue color cast the darker it became. I looked at your comment about this regarding the fact that either one of the filters might not be good, however the circular filter is an expensive Hoya HD polarizer and the linear is made by Vivitar. I went to a camera store and tried a couple of other linear filters but still got the strong blue color cast as it darkened

By: aaanouel

aaanouel — Mon, 03 Oct 2011 01:37:55 +0000

Hi Darren
It’s funny, I’ve passed though almost the same about double CPL used as variable ND filter.
I had two of them, but “el cheapo” first.
And I LOL when you mentioned High School Physics Class… Yes, I do remember that, and very clearly.

But I have just discovered that CPL filters work only in one direction: if the light comes from opposite face from what they are designed for, they just don’t work, and to combine CPLs they have to be stacked in a specific way. Stacking them in the wrong way, they will filter the light in a weird way changing the color from some yellow tint to greenish (as your previous example images) not as Neutral Density Filter.

To make it short, what I finally did was: disassembled “el cheapo”, flipped the polarized glass 180 degrees (inner face out) and reassembled again. Now, I can stack my two CPLs filters and it does work as expected: Now I have a variable ND filter also.

You may like to read my short post here.
(http://forums.dpreview.com/forums/read.asp?forum=1009&message=39490953)

Thks4sharing

By: stefan

stefan — Wed, 31 Aug 2011 18:30:32 +0000

I am new to photography…..but your pages, tips and advice are fantastic. They are so motivating.Just as I’m thinking…’sod it’ along comes your site.

thank you

stefan

By: Jyoti

Jyoti — Sat, 27 Aug 2011 16:18:16 +0000

Helpful tips. Also check out following article that has suggested use of two CPL instead of one LPL in front of a CPL.
http://www.digitalphoton.net/making-a-variable-nd-filter-with-circular-polarizers/

By: Raj

Raj — Sun, 31 Jul 2011 09:59:12 +0000

Hi, I tried the options but most of the shots having heavy blue. I bought little expensive B+W KSM CPL and B+W LPL
any special camera setting i have to do? I have pentax K-5.

By: Masao Miwa

Masao Miwa — Wed, 13 Jul 2011 14:24:43 +0000

Fantastic idea, tried it and it works great! I have been toying with using ND filters but felt I couldn’t afford the variable density filters because they were so expensive. Thanks for a very useful practical idea.