Detection of scattered light in telescopes

Institute of Physics and Astronomy, University of Aarhus, DK-8000 Århus C, Denmark

Corresponding author: Send offprint request to: F. Grundahl; fgj@obs.aau.dk

Received: 29 August 1995
Accepted: 25 September 1995

Abstract

We present a simple, but powerful method to test for the presence of scattered light in telescopes. Scattered light can seriously hamper any attempt to achieve a proper flat fielding of CCD data. The method consists of making a pinhole camera (camera obscura) by placing a pinhole mask in front of the CCD window. Exposing the CCD in this configuration gives an image of the light sources in the optical path. Tests made at the Nordic Optical Telescope have led to a reduction of large scale flat field variations due to scattered light from a total of to below by improving the telescope baffles.