The imaging properties of large reflecting astronomical telescopes

Abstract

This thesis is concerned with some of the limitations concerned with the imaging properties of astronomical telescopes of large apertures. These arise from the atmosphere, the diffracting aperture, the residual errors in the optically worked surfaces and the characteristics of the detection devices. Methods of Fourier optics are used to determine modulation transfer functions and associated point spread function. They are applied to three problems. The first of these is a comparison of the diffraction patterns that are expected from the multi-mirror telescopes. These are made either of separated individual mirrors or of segmented mirrors shaped to an overall parabolic shape. The effect of the dilution of the aperture in the former and the effect of misalignment in the latter is investigated. In the second study, the factors contributing to the imaging of the UK Schmidt telescope are considered and design studies of this and other two variants are examined. In particular the limiting effect of the atmosphere and of the detecting photographic emulsion is noted. Thirdly the overall limitation of the atmospheric seeing is considered experimentally. The Durham Polaris seeing monitor has been designed and built with a shear interferometer. It has been tested at local ground level where local measurements of seeing have been made. In the near future it will be taken and used at La Palma.