Optical system with an external aperture diaphragm for astrometric systems

The optical system of an objective that is achromatized in the spectral ran ge 0.5-1.1 mu m and has a corrected field curvature and a posterior section amounting to half of the focal distance is developed. The entrance pupil i s positioned in front of the first lens for the purpose of reducing the dim ensions of the lens shade. The models of the objective fabricated have an i mage quality close to the diffraction limit. A scheme of the relative arran gement of objectives which simultaneously project two portions of the starr y sky onto CCD arrays mounted in a single housing is presented. (C) 2000 Th e Optical Society of America.