Finder Scopes
Finders or finder scopes offer a much wider field of view than a telescope, which aids in either object location or the alignment of a go to telescope. There are two types of finders: optical or reflex. An optical finder is a small refractor typically supplying 7-9X magnification. with a five degree field of view. Optical finders with 50mm aperture are the most common, but the larger 60mm and 80mm variants are becoming popular with owners of big Dobsonian telescopes for hunting faint deep space objects. Optical finders with 50mm aperture are generally adequate for locating Messier objects under suburban skies.
Reflex finders are also know as zero magnification finders. They provide either a red dot or a series of concentric red circles that appear to be off in space. It is not at all uncommon to see both a reflex finder and an optical finder scope mounted on one telescope.