Astronomy Hacks

Tune Your Newtonian Reflector for Maximum Performance

Align your optics to provide the best possible image quality.

Collimation is the process of aligning all mirrors and lenses in a telescope so that they share a common optical axis. Awell-collimated scope provides the best images its mirror or objective lens is capable of providing. A poorly collimated scope has significantly degraded image quality—how degraded it is depends upon how poor the collimation is.

To understand how important proper collimation is, consider two telescopes of the same aperture and focal ratio. One scope has a typical mass-market Chinese mirror, accurate to perhaps 1/4 wavelength or about 0.80 Strehl. (Strehl ratio is a statistical measure of overall mirror quality based on interferometry testing; a perfect mirror—impossible in the real world—has a Strehl ratio of 1.0.) The second scope has a premium mirror, made by a master optician such as Carl Zambuto or R. F. Royce. That premium mirror may cost 5 or 10 times as much as the mass-market mirror, and it is accurate to perhaps 1/20 or 1/40 wavelength, say 0.98 Strehl. There is no comparison between these mirrors. The first is mediocre. The second is world-class.

So we set up the two scopes and point them at Jupiter or Saturn. The inexpensive scope is perfectly collimated. The premium scope is just slightly out of collimation. How do the images compare? The cheap mirror beats the premium mirror, and not just by a little bit. The cheap mirror wins hands-down. ...