What is the difference between a lens and a mirror?

A mirror is a reflective surface. Light passes through the glass and hits the silver
backing, reflecting off of it. (The angle of incidence equals the angle of reflection.)

A lens, on the other hand, does not reflect light; it refracts it. After entering the
glass, light refracts differently depending on the shape of the lens and also
creates a focal point where the refracting light comes to a point. This differs for
different lenses -- convex or concave -- which is why there are different lenses for
different types of eyeglasses.

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More reference

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