MENGUKUR ABERASI ASTIGMATISMA PADA TELESKOP RIFAST 500 F/3.8 MENGGUNAKAN METODE GEOMETRI

Currently the Ritchey-Chretien telescope is the choice of many astronomers for their observations. The Ritchey-Chretien Telescope is a reflector telescope capable to reduce comma and spherical aberrations in the resulting image, but the aberration of astigmatism still be found on this telescope. The research is about measuring astigmatism aberration on RiFast 500 f/3.8 using geometric method, that is the RitcheyChretien telescope with diameter of 500 mm and focus of 1900 mm. Luna et al. [7] consider geometry methods is simple method for measuring astigmatism on telescopes because do not require additional instruments and the results is comparable with wavefront tests. This method is based the geometric analysis of the external contour of the image of a slightly defocused star [7]. In this study two astigmatism values were obtained at two different coordinate positions valued at 258.78 nm and 300.39 nm.