Plotting spot diagram is one of the most important methods of evaluating the performance of an optical system. But it needs tracing of a great number of rays and, therefore, a lot of calculation time.
The interpolation method using the spline function makes it possible to plot the spot diagram with reduced calculation time and to determine the geometrical M.T.F. easily.
The method is applied to evaluate with high accuracy a photographic objective of semi-wide angle and of high numerical aperture.
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