Is the lens of the camera convex or concave, or both?

The lens of a camera is of course a combination of convex lens and concave lens.

You may not understand it after listening, but you studied convex lens imaging at school. Why do you need concave lenses? I just want to say:

The concave lens was first introduced because Dan Toujing has many defects, such as distortion and dispersion. In order to solve the dispersion problem, a combination of convex lens and concave lens is used.

The solution is to use optical glasses with different refractive indexes to make convex lenses and concave lenses respectively, so that they can be combined into one. Convex lens will disperse, concave lens will pull back dispersion (positive and negative effects). Therefore, the later camera lenses are all composed of convex lenses and concave lenses. For example, the Kirk lens used in Seagull 4 has two convex lenses and a concave lens in the middle (called three lenses), which is the simplest and most famous asymmetric positive lens.

There is a lot of knowledge about lenses. You can read some books if you are interested.

I think some friends don't know, so it is better to learn first. ,