Concave mirror and convex mirror are both mirrors, the difference is that the former takes the inner surface of the sphere as the reflecting surface, while the latter takes the outer surface of the sphere as the reflecting surface; The effect of the former on parallel incident light is convergent, while the latter is divergent; The former becomes an inverted and reduced real image, and the latter becomes a reduced and upright virtual image.

Both concave lenses and convex lenses use the refraction of light. The difference is that, structurally, the former is thin in the middle and thick in the edge, while the latter is the opposite; The former refracts parallel incident light and then diverges, and the reverse extension line of divergent light passes through the focus (virtual focus), while the latter refracts parallel incident light and converges to the focus (real focus); The former will always become a vertically reduced virtual image, and the latter can become a real image (when the object distance is greater than the focal length) or a virtual image (when the object distance is less than the focal length, the virtual image is vertically enlarged).