Mammoth Memory

Concave lenses – centre of curvature

If you take a clear rectangular block of plastic and cut two circles out of the block as follows:

Concave lens formed by removing 2 circles from a plastic block

you get a concave lens.

This is great news because this is a terrific way to remember that a concave lens has two centres of curvature (two centres, one in each of two spheres).

The centre of curvature of a concave lens

Centres of lens curvature are usually denoted with a `C`.

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