> A 20mm lens is not an excellent portrait lens. It will make your face look fatter.
It depends on the sensor size. A 20mm lens in (35mm) full-frame is a very wide lens. A 20mm lens on a Canon/Nikon DSLR is the same as a 35mm lens on a (35mm) full-frame. A 20mm lens on a point-and-shoot is even "longer".
In a (micro)4/3ds camera, 20mm is equivalent to 40mm in 35mm, which is close to a normal lens. It's on the short end for portraiture, but you can get nice results if the lens is fast enough.
It depends on the sensor size. A 20mm lens in (35mm) full-frame is a very wide lens. A 20mm lens on a Canon/Nikon DSLR is the same as a 35mm lens on a (35mm) full-frame. A 20mm lens on a point-and-shoot is even "longer".