neutral density filters

[russrad]

Hi
has anyone had any success making a variable neutral density filter using 2 circular polarisers?
see here: http://www.petapixel.com/2010/08/27/how-to-build-a-cheap-and-simple-variable-neutral-density-filter/

You can also make an ND using a circular polariser and a linear polariser - this looks like it maybe be less trouble.
http://www.digital-photography-school.com/create-your-own-variable-neutral-density-filter

I thought I'd give it a go this weekend

Russ

[andylo]

Without looking in the details inside the link....

1) stacking 2 x CPL MIGHT introduce unwanted vignette? I know some people are very good landscape photographer using a telephoto lens but I always use a UWA and even a non-slim rim filter will introduce vignette in my shot.

2) Isn't linear polarizer very likely to stop the AF works in majority of SLR? (not the mirror-less camera)

3) Finally, 6 x ND filters probably is cheaper than 2 x CPLs :p

[OzzieTraveller]

G'day Russ

Yes mate - I have tried this several times
Problem - massive colour shift into the magenta/purple spectrum

gave up after that ... can post an image if you want to see

Regards, Phil

[russrad]

Thanks for these replies.
I was thinking that one filter might be more convenient than my cokin filters, but if you have to unscrew the filters to focus then there is no advantage- I hadn't thought of that.
Yes, vignetting will be an issue for sure - even on my 16mm
Massive color shift - doesn't sound good.
Looks like this isn't worth the trouble.
cheers, Russ

[peterb666]

I was under the impression that you used a circluar polariser and linear polariser to do this.

As for AF not working, I wouldn't think it was an issue as it wouldn't work very well anyway once you have whacked on 4 or 5 stops plus of light stopping. MF has its uses.

[reaction]

You can buy variable neutral density filters, but the small small small print will tell you:

at wide angles you only get max ND2
at certain ND settings you get radial lines in your shot - which you won't see until after your 5min exposure!