How many kinds of external lenses are there? What's the use of each?

Mainly depends on what classification you ask.

First, according to the characteristics of focal length, it can be divided into fixed focus lens and zoom lens.

Second, from the size of the focal length: fisheye, ultra-wide angle, wide angle, standard, medium focus, telephoto, ultra-telephoto, macro, axis shift and distance increase.

Thirdly, from the interface mode: Canon's EF port, Nikon's AF port, Sony's A port, Pentax port, 4/3 port M4/3 port.

Fourthly, focusing mode can be divided into driving motor and non-driving motor.

Five, from the zoom mode, it can be divided into telescopic zoom and periscope zoom.

In addition, there are also points with and without anti-shake. . . . . Wait a minute.

What's the use of asking each other? The problem is too big. What kind do you mean?