Toronto Photography Meetup Group

Has anyone here tried using wide angle lens adaptors like the one here?

http://photojojo.com/store/awesomeness/ ... acro-lens/


I don't have the need to use a super wide angle lens often enough to justify buying an actual lens, but I'm considering buying this for the rare cases where I do need one. If I do get it, it'll mostly be used on the Sigma 17-70mm which has a thread size of 72mm. The thing I'm worried about is that using the adaptor on a lens with such a large thread size may cause some extra vignetting (I mean on top of the normal vignetting that comes with using an adaptor).

What do you guys think?