How do you test a new scope to ensure it's up to spec?

[SiD the Turtle]

Hi folks,

Got a new refractor on its way to me, but as a relative beginner I have no experience in knowing what I'm looking at in terms of it being correct on arrival. How do you test your new scopes for astrophotography in particular?

Of course the answer is probably look down the scope/take pictures and see if the stars are round, are they clipped, any fringing or colour distortion etc. But are there any more scientific ways of testing? To spot things as a beginner I might not spot?

I have seen some people post images that almost look like heatmaps or heightmaps, which of course I'm struggling to find now I'm looking for them!

[vlaiv]

For quality of optics - there is a star test.

It is performed with scope thermally stable with high power eyepiece in a good seeing, by looking at diffraction patterns both side of focus (out/in focus) as well as in exact focus. Reading star test is not easy, but some things can be noticed rather quickly - like pinched optics, collimation issues and such.

Alternative to this is to perform Roddier analysis - which is the same thing except you take image of out and in focus patterns and let computer software (WinRoddier) perform analysis for you.

You can also take a image of star field and use software like CCDInspector or similar to produce FWHM/HFR maps that will tell you about field curvature, any potential focal plane tilt and similar (it what you refer to as heat/height map). Alternative to this of course is just examining star shapes in the corners of your image and figuring out yourself if there is any issue with your optical train.

[SiD the Turtle]

Thanks @vlaiv, given me some new concepts to read up on/Google, much appreciated.