Limitations of ground based near and far infrared astronomy

Abstract The possibilities of ground based infrared astronomy are discussed. It is shown that telescopes used up to now are not optimized and that the Diffraction Limited Detectivity conditions (DLD) cannot be reached, in the near infrared, by the larger telescopes. The maximum useful diameters for near i.r. and far i.r. telescopes have been evaluated and a new parameter (i.e. visibility) is introduced in order to describe the performances of i.r. ground based telescopes.