Oops! I forgot something in the fisheye review, and have now added it towards the bottom.
The Vivitar 7mm F/3.5 fisheye lens covers a larger area than the full frame Sony 16mm F/2.8 fisheye, used on a full frame camera, in this case the A900. It’s noticeable right off if you have both lenses. The full image below is from the A580 and Vivitar, and the orange crop mark is the coverage area from the A900 and Sony 16mm fisheye. This comparison is just for fun as it makes no sense to use either one on the other format. I think it’s great the APS-C lens has a larger coverage area, that make the Vivitar even more useful and fun!
This boring image does not take advantage of the fisheye effect, it just makes the Saguaro cactus look crooked, but I took both cameras and lenses with me on a hike to test them out, and decided to see the coverage differences at this point along the trail—and here you are.