title: Cassegrain telescopes: limits of secondary movement in secondary focusing.
abstract: The maximum distance to which the secondary mirror can be moved with respect to its primary in a true Cassegrain telescope with limited image deterioration is found to be proportional to the fourth power of the focal ratio of the primary mirror. This limit is independent of all other parameters describing the system when the magnification of the secondary is greater than about 3.
authors.forename: R N
authors.initials: RN
authors.lastname: Clark