Optical coating

[tickmatrix]

Is there any way to check that an optical coating is OK? 

[ollypenrice]

Look through it.  You can also look at it but it's important to remember that looking at optics is not how we use them. In the last quarter of a century I've looked through, or imaged with, a tiny handful of optics which looked perfect. But I've used dozens which performed perfectly. One of the best SCTs I ever looked through had an as-yet uncoated corrector plate because the builder hadn't yet got to that stage...

Olly