This is a diagonal fisheye: it fills the entire rectangular frame of your photograph with a fisheye image that is almost 180° measured corner-to-corner. It’s about the equivalent of a classic 15mm fisheye on a full frame camera.

It’s very sharp and has the unusual ability to focus a few inches in front of the glass, meaning you can shoot a fisheye macro basically. I can’t for the life of me figure out why you would want to do that, but now you can.

We get asked a lot (and even worse, not asked by people who don’t know) what the different focal length fisheyes look like on different cameras. Here’s the short summary:

• 4.5mm – is a circular image in the center of your picture on a crop frame camera. A very, very small circle on a full frame.
• 8mm – is a circular image in the center of your picture on a full frame camera. Nearly, but not completely fills a crop frame.
• 10mm – is the classic, corner-to-corner fisheye look on a crop frame camera. Doesn’t fill a full frame image.
• 15mm – is the classic, corner-to-corner fisheye look on a full frame camera. Slightly fisheye look on a crop frame.

The image below should give you an idea of what you get with each type of camera.