Astronomy Hacks

Star-Collimate Your Scope

Align your scope perfectly using the properties of light.

Collimation is the process of aligning a telescope so that all of the mirrors and lenses share a common optical axis. In order to provide the best possible images, a scope must be collimated perfectly. Not just “collimated pretty well” or even “almost-perfectly collimated.” An almost-perfectly collimated scope may show you 50% or less of the detail that is visible when collimation is dead-on.

Just as no pianist would play an untuned piano, no astronomer should observe with an uncollimated scope. And yet, very few astronomers collimate sufficiently often or sufficiently well to get the best performance possible from their scopes. Newbies never collimate. They’re afraid they’ll muck things up beyond repair. SCT and refractor owners seldom collimate. They’re convinced their instruments don’t require frequent collimation. Newtonian owners generally collimate fairly frequently, but most simply use a sight-tube/Cheshire and/or a laser collimator to get their scopes roughly collimated and then declare the job Good Enough. They’re all wrong.

No physical collimation tool can ensure anything more than a rough collimation, and that’s simply not good enough. The only way to collimate a scope properly is to defocus a star and observe the patterns that exist on both sides of proper focus. That’s true for two reasons. First, physical collimation tools are accurate to only a few tenths of a millimeter, while starcollimation ...