Precision astrometry with schmidt telescopes

Schmidt telescopes currently provide nearly the only means to obtain positions of faint objects with respect to the standard ICRS reference system. However, the lack of adequate astrometric calibration methods to account for the specific properties of Schmidt telescopes leads to residual systematic errors of up to 1″. The main source of systematic errors is plate bending during exposure. A high-precision reduction technique to account for this effect is proposed. Application of this technique to observations acquired with the Schmidt telescopes of the Palomar and Anglo-Australian Observatories reduced the systematic errors by a factor of 2.5 and gave them a simpler structure, while simultaneously decreasing the number of unknowns in the reduction model threefold. Application of the new method, with appropriate account for the design of the particular plateholder used, will make it possible to use Schmidt telescopes to determine high-precision positions for virtually all objects detected in photographic surveys.