What are fisheye, wide angle, fixed focus, shifting axis and portrait head?

This is a shot divided from several different angles or standards.

Let's talk about a fixed focus lens first. A lens with a fixed focal length is a fixed-focus lens. This is the simplest.

A wide-angle lens is a lens with a shorter focal length and a larger viewing angle than a standard lens (35mm lens). Common wide-angle lenses generally have a focal length of 20mm up and down, and some have fixed focus and zoom.

The fisheye lens is a special wide-angle lens, with a focal length generally below 16mm and a viewing angle close to 180 or even larger. The most standard fisheye lens, the image is completely circular, and the viewing angle is 180 degrees.

Shift-axis lens is a kind of lens with tilt angle and offset function, that is, it can bend and swing in a certain range. Shift-axis lens can correct perspective deformation and adjust focal plane position.

Portrait lens is a lens for shooting portraits of people, generally a fixed-focus lens with medium telephoto and large aperture.