Depends on the filters. With high quality filters, there won't be much optical effect. Vignetting is the main risk, in that case. I am able to stack a B+W Slim CPL filter onto a B+W XS-PRO mount (also a slim mount, but with threads) on an EF-S 17-55mm without vignetting. But, if either was not a slim mount, vignetting would be a problem, and if both weren't top quality filters, there would be optical effects.