How to make a fisheye lens?

Cut off the bottom of the jar, make a hole in the middle with a needle, and cover it on the lens interface of the fuselage, which can take a "pinhole photography" effect with a large field of vision. The size of the hole needs trial and error to find the most suitable size in order to get the clearest picture quality. This is the cheapest solution. Of course, other materials can be used instead, such as plastic plates and metal plates.