Spherical Mirror Focal Length

\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

Focal length

Radius of curvature

Derivation

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

Your notes

0/5000

Other optics formulas with the same quantities

Thin Lens Equation (Lenses) shares Focal length
Lensmaker's Equation (Lenses) shares Focal length
Lens Power (Lenses) shares Focal length
F-Number (f-stop) (Optical Instruments) shares Focal length
Depth of Field (Optical Instruments) shares Focal length

Where this formula is listed

Optics formulas, under Reflection, alongside Law of Reflection, Mirror Magnification and Fresnel Reflection (Normal Incidence).
In the optics list it comes after Fresnel Reflection (Normal Incidence) and before Snell's Law.
Optics formula sheet, one of 34 formulas printed with symbol keys and SI units.
The full formula index, grouped by category and topic.

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.