Автор: митко
Дата: 17-09-14 22:15
Това са най-добрите снимки през последните години. Повече подробности за камерата тук
5.1 Optical concept and design: the Three-Mirror Anastigmat
A flat-field, three-mirror anastigmat system, TMA, is adopted for the NAC. Anastigmatism (freedom from third-order spherical aberration, coma, and astigmatism) is attained by appropriate aspheric shaping of the three mirror surfaces, and a flat field (zero Petzval sum) is achieved by appropriately constraining the system geometry. Our solution (Dohlen et al., 1996) has an axial pupil physically placed at the second mirror M2, an off-axis field of view, appropriate baffle performance and a large back-focal clearance. The optics requires only two aspheric mirrors, the tertiary remaining spherical. This considerably reduces fabrication cost and alignment difficulty. The three mirror surfaces are rotationally symmetric about a common optical axis, but the field of view is sufficiently removed from the axis to ensure that all rays pass through the system without vignetting. The mirrors are made of silicon carbide; details of their fabrication, polishing and alignment can be found in Calvel et al. (1999).
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