I just purchased the Zeikos fisheye lense for my

The 50 mm lens is a full frame lens, and the D80 is a DX camera. This means that the 50mm lens puts an image out that is bigger than what the D80 can "see". The good part of this is that the D80 (and most of the other Nikon DSLR's) use only the image from the center part of an older lens. The bad part is that if you put the fisheye filter on it, the fisheye effect that is mostly seen at the edges of the lens doesn't show up on the D80 sensor. If you could put the fisheye filter on a DX lens, it would give you the full effect.