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Optics
Optics

Spherical Mirror Focal Length

1f=2R\frac{1}{f} = \frac{2}{R}

The focal length of a spherical mirror is half the radius of curvature. This is the reciprocal form of f = R/2.

Variables

f
Focal length
m
R
Radius of curvature
m

Derivation

Derived using paraxial approximation for rays close to the optical axis reflecting from a spherical surface.

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Common questions

What is the Spherical Mirror Focal Length formula?

Spherical Mirror Focal Length is written 1/f = 2/R. The focal length of a spherical mirror is half the radius of curvature. This is the reciprocal form of f = R/2. It belongs to Optics, under Reflection.

What are the units in 1/f = 2/R?

In SI units, f is focal length, measured in m; R is radius of curvature, measured in m.

How is the Spherical Mirror Focal Length formula derived?

Derived using paraxial approximation for rays close to the optical axis reflecting from a spherical surface. The result is 1/f = 2/R.