Lens Formula & Design Aids
General guidelines for choosing a particular lens type for a specific application are given along with the standard part tables in the followings sections. Complete detailed optical design service for complex optics or systems is available from Janos Technology. Fees are often waived for products we manufacture. Below we show calculations to determine radii of curvature for a given spherical or cylindrical lens type.
Shown on these sketches are the Effective Focal Length (EFL), the Back Focal Length (BFL), the Center Thickness (CT), [and the locations of the element’s Principle Points (P1 and P2)].
The radii of curvature R1 and R2 refer to the left and right surfaces respectively. R1 or R2 is positive (negative) if the center of curvature is to the right (left) side of the lens. The EFL is positive (negative) if the focal point is to the right (left).
The lens maker’s equation for a single element in air is:
Here’s the index of refraction for the material at the design wavelength. In most cases this can be approximated by the Thin Lens Formula:
The BFL (the distance from the center of the second surface to the focal point) may be found from: