Ultra wide angle lens the difference is only whether distortion is present or not. However, the shorter the focal length, the more difficult it is to implement rectilinear correction. In fisheye lenses, the visual angle is close to or more than 180 degrees in at least one direction. For example, a "diagonal fish eye" would have a viewing angle of at least 180 degrees within the diagonals of the frame. A "circular fisheye" would represent the image in the form of a circle. Rectilinear ultra-wide angle lenses are used in photography and cinematography sometimes to achieve three-dimensional perspective distortion instead of simply two-dimensional barrel
Six Degrees patent Zynga and Tribe.net for $700,000 at an auction in 2003. When explaining his reasoning for purchasing the Six Degrees patent, Hoffman stated, "Right now you're hearing a lot of spurious patent threats (...) And that's why I moved quickly to get a patent that was foundational." He also commented on other entrepreneurs' views of social networking: "The general attitude among entrepreneurial people is that they think that they were first and that there is no history to what they are doing (...) Both Mark and I had tracked six degrees as an intellectual precursor to our own businesses." Andrew Katz