Testing Strehl & optics of scopes

[Emuhead (Andrew)]

Hi all,

Are there ways, or services available to people, to scientifically check the optics of their scope?

Do people do that even?

I'm curious to know and wouldn't mind running a test of some kind.

[Atmos (Colin)]

PixInsight has a tool for this where you take intra and extra focus images. Not sure on its accuracy but it’s there.
That’s all I got!

[glend (Glen)]

A Ronchi eye piece can tell you alot, and you should be able to track down details on glass used (if it is a refractor). There are charts available online that show test details of different glass element combinations typically used in refractors. Some Newt builders, like GSO, publish details on their mirrors, many other do not, but again a Ronchi eye piece can tell you alot in that case. Have a look at the Gerd Neuman test photos taken through Ronchi EPs.

[Peter Ward]

To answer your question, yes.

A number of manufacturers also supply quantitative test data with their optics, some test their optics but do not supply it to the customer (eg Astro-Physics as many can mis-interpret the data), and some manufacturers only guarantee your satisfaction and not the quality of their optics.

As far as Australia goes. Sadly I am not aware of anyone who does inteferogram testing of optics.

As a ball-park however, the "Star Test" detailed in Dick Suiter's book is an excellent resource, and well worth a read on how to perform.

[Emuhead (Andrew)]

Ok thanks guys, that helps.

I'll try the pixinsight method first, and perhaps go from there. I was thinking I might be able to verify the manufacturers results, just because why not. But if it's not a thing people do really, I'll leave it also.

It would be a useful service to offer people though if you had access to an interferometer as there could be a market for this. People spend loads on scopes, would be nice to verify the optics, aside from pixel peeping.

[Stefan Buda]

The pixinsight method is based on the Roddier test. The Roddier test was used to characterize the HST fault in orbit and it is almost as good as a full interferometric test if done carefully. It recreates the Zernike polynomials that describe the wavefront and produces all sort of graphical representations, like synthetic interferogram or wave front error.
The software is free and the learning curve not steep if you understand optics.