On the astrometric use of the prime focus of the Isaac NewtonTelescope with the Wynne field corrector
The results of measurement of 23 plates taken on the Pleiades with the Isaac Newton Telescope through the Wynne prime focus field corrector are discussed. Coefficients of radial distortion terms, including cubic and fifth powers of the radius are derived using the star positions in the catalogue of Eichhorn et al. as a standard reference frame; these values agree well with the values predicted from the design parameters. It is shown that the astrometric accuracy of the system is as good as that generally achieved with conventional long focus refractors.