Simple and accurate method for determining lens focal length

A simple and accurate method for determining the focal length of a lens is presented. There is no need to know the distance between lens principal planes and can be performed with easily available and inexpensive hardware. Depending on the test lens (TL) f-number, the error on determining focal length can be in the order of 0.1% of the focal length. We discuss determining focal length with the Newton equation f(2)=zz('), with the Bessel equation f=((L-PP)(2)-D-2)/4(L-PP), with equation f(2) = y(')(y + y(')), or with equation f = (y(2) - PP2)/4PP. (c) 2023 Society of Photo-Optical Instrumentation Engineers (SPIE)

Automated summary

A simple and accurate method for determining the focal length of a lens is proposed in this paper. The method does not require knowing the distance between lens principal planes and can be conducted with readily available and inexpensive hardware. Depending on the f-number of the test lens (TL), the error in determining the focal length can be as small as 0.1% of the focal length. The paper discusses several equations, including the Newton equation, Bessel equation, and other equations, for determining the focal length.