Refractor vs. Reflector

Mirrors vs. Lenses

(a) A refracting telescope uses a primary lens to focus starlight into an image that is magnified by a lens called an eyepiece.   The primary lens has a long focal length, and the eyepiece has a short focal length.  The incoming light is refracted or bent by the lens system.

(b) A reflecting telescope uses a primary mirror to focus the light by reflection.  A small secondary mirror reflects the starlight back down through a hole in the middle of the primary lens to the eyepiece.   There are many variations to this basic reflector, the Newtonian, the Cassegrain, and the Schmidt-Cassegrain.  The incoming light is reflected by the mirror system.

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