Lens/Mirror Eqns & Conventions

• We have derived, in the paraxial (and thin lens) approximation, the same equations for mirrors and lenses:

when the following sign conventions are used:

Variable

f > 0

f < 0

s > 0

s < 0

s’ > 0

s’ < 0

Mirror

concave

convex

real (front)

virtual (back)

real (front)

virtual (back)

Lens

converging

diverging

real (front)

virtual (back)

real (back)

virtual (front)

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