Sigma 12-24 Any way to polarize?

I'm thinking about getting the sigma 12-24 for the 5D and to use occasionally on a 30d as well. I know the lens accepts gel filters, but do they make polarizers in gel filters? Obviously, i'd be using a circular polarizer if I could, but considering the lens is all bulbous, that just wont work.

what do i do? are gel filters really useful at all?

I really don't think a gel polarizer is practical. The polarize the light you need to elements - one to rotate relative to the other. I sure can think of a way to do that in a gel holder.

Mark

It's difficult... the front lens cap is in two parts, a "tube" that goes on the outside of the lens barrel and a regular cap that in turn goes on the front of that tube. I've seen two ideas for filters, either attach a round one to the tube, a second solution was that one of the filter systems (not Cokin, one of the others) has a holder that fits around the outside of the tube. Both solutions will vignette on the 5D but may work on the 30D. I don't know if my explanation makes sense...

Either way, but maybe beside the point, you may not like the effect of a circular polarizer on such a wide lens anyway as you get a quite uneven effect across the image.

I think that is true only when discussing circular polarizers, and there are certainly linear polarizers as well. Polarized sunglasses for instance do not have two elements.

I think there would be a LOT of vignetting if I attached a standard cir polarizer to the front of the tube part of the lens cap. I have the 15mm sigma fisheye and it has the same type of lens cap. If i just take the cap off and leave the tube part on it is like looking through a tunnel....i'd say almost 50% of the image is taken up by the tube.

would a cokin or lee filter be big enough to cover the area needed? Considering such a large angle of view, I would think you'd need a very large cokin filter. anyone have any experience with this lens and those type of filters? this would also apply to nd grad filters as well...

I am buying this lens mainly for the 5d, so it would need to work with the 5d.

thanks for the input/ideas.....anyone else?

Here's someone's DIY solution:

http://www.dslr.co.uk …filter_on_12-24/index.htm

Contact Sigma and ask for their recommendation. After all, a wide angle and a CP kinda go together so they must have a recomendation. I had a the 15-30mm EX which is very nice and there is a thread for a CP/filters on the tube but I never tried it. You could maybe try one in a shop and check the shots. 12mm would be crazy wide on a FF. Do you need that?

I'm not sure they make gel polarizers for the rear element.
Hence, I wouldn't count on it.

need? who knows.

want very badly? yes indeedy!