So, I was thinking of picking up two really cheap OEC brand Linear Polarizer filters and making a 77mm to 77mm adapter by gluing two 77mm cokin Mount rings together face to face with the threaded sides out.

I realize it will vignette, but If this is what a variND filter is, it should work.

Also, I probably wouldn't use it for anything serious, because OEC filters are supposed to suck but it seems like it would be pretty cool if it actually worked.

Found this thread http://digital-photography-school.co...ensity-filter/

I guess you only need a Linear polarizer and a circular polarizer.

Yeah a CP behind the first LP will work. Either will work though.

Singh-ray makes a filter like this, quite expensive though. Pretty sure this concept came up in discussion here late last year when I first started talking about the high density ND filters.

Originally Posted by emorphien

Yeah a CP behind the first LP will work. Either will work though.

Singh-ray makes a filter like this, quite expensive though. Pretty sure this concept came up in discussion here late last year when I first started talking about the high density ND filters.

I have seen the Singh-Ray version, spendddddy

there is no reason why this wouldn't work, probably very well. i don't even think you're going to get a lot of vignetting issues.

of course the normal polarizing effect would be present and could not be removed, unlike a "plain" ND.

test out a proof of concept with cheap filters, then consider scaling it up if it works well. hell, if they dont already exist, get an M-M adapter made up so you can do your own stacking and sell it on ebay.

Someone makes a version of this where the front polarizer is reversed if I recall, and has the 1/4 wave plate first.