Proceedings PaperOptical Design Of ISOCAM
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The Infrared Space Observatory Camera (ISOCAM) is one of four instruments attached to the ISO satellite due to be launched by an Ariane 4 rocket in 1993. The camera is designed to operate at 4K and uses two channels to cover the spectral range from 2.5 to 17 μm. Geometrical aberrations and diffraction were studied by a complete ray-tracing of the system including the f/15 Ritchey-Chretien telescope. Curvatures, aspheric coefficients and positions of the various optical components are optimised to reduce spherical as well as off-axis aberrations (coma and astigmatism). Chromatic aberrations are reduced by a suitable choice of infrared materials: Germanium for the 5 to 17 μm range and silicon for the 2.5 to 5 μm. A Monte-Carlo statistical approach was used to evaluate the effect of manufacturing and assembly errors on the 90% encircled energy diameter of the Point Spread Function. Special effects as deformation and possible existence of ghost images in the system are presented. A test facility including a f/15 simulator and a cryogenically cooled camera simulator has been developed in ROE to test the optics at 4K by measuring its PSF. Recent measurements show a good agreement with the computed PSF.