Star Testing a Refractor....

[skye at night]

Diagonal or no diagonal?

Steve

[brianb]

Star testing only makes sense if the seeing is at least very good, that only happens near the zenith so, unless you already have a cricked neck or want to acquire one, a diagonal is probably a good idea. But be aware that the diagonal is part of the optical train & will add its own "flavour" to the view, unless it's optically impeccable.

[Merlin66]

Best to do it without the diagonal.. another layer of possible problems, but as Brian says... easier said than done!

One good solution is to use a webcam to look at the star image.

There are some good software packages to assist in the analysis.

roddier : Roddier Test

Ken