Question

A PLANO- CONCAVE LENS AND A PLANO-CONVEX LENS ARE PLACED SUCH THAT ONE IS FIT INTO OTHER COMPLETELY. IF RADIUS OF CURVATURE FOR CURVED SURFACE FOR BOTH THE LENSES IS R AND THE LENSES ARE DIFFERENT MATERIAL N1 AND N1. WHAT WILL BE THE EQUIVALENT FOCAL LENGTH OF THIS COMBINATION.

Answer 1

Plano-concave lenses diverge a collimated beam from a virtual focus and are commonly used in Galilean-type beam expanders. Given their negative focal length and negative spherical aberration, plano-concave lenses can be used to balance out aberrations of other lenses in the system. Thorlabs provides plano-concave lenses fabricated from N-BK7, N-SF11, UV-fused silica, calcium fluoride, and zinc selenide. N-SF11 offers a usage range that is slightly shifted to the red compared to N-BK7. However, N-SF11 glass is associated with more dispersion because it has a lower Abbe Number than N-BK7 glass. For more information on these substrates, please visit our Optical Substrates page.
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