So I am traveling to Europe for 6 weeks for a study abroad program. I think it would be fun to shot with a fisheye lens. I have a Canon 20D with 17-85mm lens and my question is should I just get a screw on lens thats 67mm for about $100 or so? I know they do have a lot of fall off, but thats my idea. If anyone could help me out and made post some info if they have used a screw on, or if someone could post pictures. Thanks.