i found a fisheye 15mm for cheap but its only for film, is here attachments that i can buy so that the sigma lens made for the film can screw into my canon 20d?
Probably not. First, the lens needs to have the right Canon mount. Even lenses made by Canon don't all fit the newer digital camera. Then, unless the camera has the full frame sensor, the edges in the image will be clipped off, which means it won't work as a 15mm fisheye, but more like a regular wide angle lens.
