A discussion on infared astronomy - Large flux-collectors for infrared astronomy

Abstract

Astronomical telescopes can be used in two principal ways. One is to collect radiation and feed it to analysing apparatus, such as a spectrometer, photometer or polarimeter. The other is to image an extended region of the sky onto an image-detector such as a photographic plate. These functions are complementary, and the choice between them depends on the purpose of the observations, the kind of object under investigation, and the available intrumental resources. In field imaging, the rate at which information can be collected is proportional to the product of the squares of the aperture and the field diameter of the telescope (Fellgett 1964). The Schmidt configuration gives by far the largest field of any telescopic system which we now know how to design, construct and keep in adjustment. Other systems are known, for example Schmidt-Cassegrains, which can have higher theoretical performance, but the problem of maintaining their components in sufficiently good alinement during fabrication and use is as yet unsolved, though almost certainly soluble by further research.