Assertion: collimator's axis | /r/HasProperty | aimed at the center of the main mirror
Facets:
value: for best performance
type: PURPOSE
Source sentences:
text: Like the primary mirror, the eyepiece has an optical axis, and this axis should be aimed at the center of the main mirror for best performance — though in practice it is the center axis of the focuser drawtube that you aim at the primary mirror.