A computer program has been written to rapidly calculate stray light in optical systems using the IBM PC. The program
calculates the Point Source Transmittance by either of two methods. The first method uses formulas requiring only firstorder
system parameters such as F-number, aperture diameter, primary Bidirectional Scattering Distribution Function,
and baffle tube length. In the second method, paraxial rays are traced through the optical system and the program
evaluates scattering from all of the optical surfaces. Stray irradiance at the focal plane of an optical system from an
extended source such as the sun or the earth can be calculated by integrating the incident irradiance over the source,
weighted by the Point Source Transmittance. The result is then multiplied by the integral of the system spectral
transmittance function weighted by the blackbody function. The program also computes veiling glare, ghost images,
narcissus, spectrally weighted transmittance, and illuminance and spectral luminance using the photopic and scotopic
spectral efficacy functions. Blackbody-related functions including radiance contrast are also computed. Good agreement
is obtained between GUERAP III and SOAR for Point Source Transmittance calculations.
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