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ay45c3-page15 - D δl δθ δθ d L This is the basic\prime...

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Unformatted text preview: D δl δθ δθ d L This is the basic \prime focus" astronomical telescope. The detector (CCD array) goes at the focus. The \image scale" is the ratio of physical distance at the focus to angular distance in the sky, and it depends only on the focal length (see gure), l = L or  = 1=L :  l For example, the 16.8 m focal length of the Palomar 200 inch corresponds to 12 arcsec/mm (check this!) The eld of view is determined by the focal length and the size of the detector (d in the gure) FOV = d=L : In the above example, a CCD array of diameter 60 mm = 6 cm would have a eld of view of 1 60 mm  12 arcsec  60arcmin = 12 arcmin = 0:2 : 1 mm arcsec What is the relation between the surface brightness of an object in the sky (a planet or galaxy, say) and the ux (energy per area per time) in its image on the detector? We multiply I by the area of the lens (mirror) and 39 ...
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