A technique for the optical characterization of imaging air-Cherenkov telescopes

A procedure for the optical characterization of imaging air-Cherenkov telescopes IACTs is discussed. The method relies in simple principles of geometrical optics. A CCD camera provided with a lens and located at (or near) the telescope focus records images of the mirror while the pointing direction of the telescope moves around a star. For each image, the slope of those mirror points which are recorded bright, due to the light star, can be accurately measured by the simple application of the reflection law. This procedure allows the reconstruction of the slope map of the mirror and thus it provides a full optical characterization. The applicability of this technique to typical IACTs is discussed by means of a simple simulation. The slope map could be reconstructed with an uncertainty better than 0.1 mrad. Many geometrical features of the mirror like facet misalignment and structure deformations could be measured with this technique.