OPHIR BeamSquared, User Manual

Page: 102 / 112

Appendix A Lens Calibration Adjustments
A.1 Plano convex Lens Calibration
When a lens is used at a wavelength different from the calibrated wavelength, a correction needs to be made.
Equation 15 provides the formula for calculating the new focal length. Do not apply these equations to
achromatic lenses.
𝑓
𝜆
=
𝑓
𝑐𝑎𝑙
(𝑛
𝑐𝑎𝑙
− 1)
(𝑛
𝜆
− 1)
Where:
𝑓
𝑐𝑎𝑙
The measured focal length of the lens at the calibration wavelength
𝑓
𝜆
The calculated focal length of the lens at the desired wavelength
𝑛
𝑐𝑎𝑙
The index of refraction of the lens substrate at the calibration wavelength
𝑛
𝜆
The index of refraction of the lens substrate at the desired wavelength, λ
Section A.2 provides index of refraction values for common lens materials at various wavelengths.