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Lesson: Chapter 5 — Optics

5.4.1. Convex lenses 1 of 4

Principal axis and optical centre

The two surfaces of a convex lens can be treated as parts of two imaginary spheres.

Figure to be added

Figure 5.33 — two overlapping dashed circles with centres C1 and C2; the lens is the shaded overlap, its surfaces A and B, with the principal axis through both centres.

Principal axis

The straight line joining the two centres. It meets both surfaces at right angles, so rays along it pass straight through without bending.

Optical centre (O)

The midpoint between the two surfaces, inside the lens. Any ray through it passes straight through without bending.

Rays through the optical centre O of a convex lens, passing straight through without bending.