Rear gel filter for 17-40L?

[squaresnappr]

Anybody use gel filter for the 17-40L and have good experiences with them? I have googled it and have not found out too much about them. I can't really find a place here in Canada that has them. I went to Henry's here in Toronto and they didn't have them. They didn't even know what I was talking about.

I use Cokin filter set and I know about the color cast issue but I was wondering what are the benefits of using the gel filters in the rear.

[Jon]

Couple of reasons - it's easier and cheaper to get gel filters and cut them down for rear mounting than it is to get the large diameter filters you'd need for typical UWA lenses. And the rear filter won't vignette like regular (not slim) filters may on a UWA. That said, there aren't a whole lot of filters you need in digital photography, and straight ND is about the only one of those I could see using as a rear filter mount. Polarizers and ND grads, the other types, need to be accessible so you can adjust them for the scene.

[squaresnappr]

Couple of reasons - it's easier and cheaper to get gel filters and cut them down for rear mounting than it is to get the large diameter filters you'd need for typical UWA lenses. And the rear filter won't vignette like regular (not slim) filters may on a UWA. That said, there aren't a whole lot of filters you need in digital photography, and straight ND is about the only one of those I could see using as a rear filter mount. Polarizers and ND grads, the other types, need to be accessible so you can adjust them for the scene.

Thanks, I see why they are not that very popular in digital photography.