PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Geometrical optics and imaging · Geometrical optics and imaging
What an Instrument Can See, Ch Pupils: the aperture of a linear system
Problem
Two microscope objectives are compared.
((a)) An oil-immersion objective is designed so that its marginal ray leaves the specimen, immersed in oil of refractive index n=1.515, at a half-angle θ=41.3∘ to the axis. Compute its numerical aperture.
((b)) A dry objective of similar construction (no immersion medium, n=1) achieves a larger half-angle θ=60∘. Compute its numerical aperture.
((c)) State which objective has the higher numerical aperture, and explain why the objective with the smaller ray angle can still have the larger NA.