Assertion: telescope's instrument | /r/HasProperty | mounted at a cassegrain focus
Facets:
value: below the primary mirror
type: LOCATION
Source sentences:
text: Instruments can be mounted at a Cassegrain focus below the primary mirror; at either of two Nasmyth focal points in enclosures on the sides of the telescope mount, to which light can be directed with a tertiary mirror; or at the prime focus in lieu of a secondary mirror, an arrangement rare on large telescopes, to provide a wide field of view suited to deep wide-field surveys.