
13.4.
Grating Efficiency
331
Fig. 13.5. An immersed echelle with a prism to couple the incident light beam to the echelle.
13.3.C.
COMMENTS ON LARGER RESOLVING POWER
One of the consequences of the relations for resolving power in Tables 13.1
and 13.2, given ^ a di/D, is the requirement for larger gratings and echelles on
larger telescopes, simply to keep the resolving power constant. Not surprisingly,
there is continual pressure to increase ^, even for larger telescopes, as demands
are felt for more detailed spectroscopic study of astronomical sources.
The available parameters for increasing ^ of an echelle on a telescope of a
given D are large ...