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The All Sky Automated Survey - Prototype Camera Lens

The Prototype Instrument of the All Sky Automated Survey is equipped with the Sigmatel 135mm f/1.8 telephoto lens. Overall condition of the lens is good (even though it was second-hand purchase), but its optics is not the best: Point Spread Function (PSF) is "triangular" rather than axi-symmetric, with two unpleasant "fingers" (see image) Full Width Half Maximum (FWHM) of the PSF profile is about 2.5 pixels (30 arcsec) at the best focus, so we don't need to de-focus instrument to get proper sampling of the star images. Fortunately PSF is constant over the whole 3 deg x 2 deg field of view.