Checking your etalon

[moriniboy]

Just been emailed this piece of information re checking your etalon (mines a PST).

If you have any doubts re the performance of you Ha scope might be an idea to check this (you will need to strip it down to the bare etalon though)

I have checked mine and its perfect, I did not expect to see any problems as its performance on proms etc. is very good.

If you look through the etalon (with it just in front of your eye so you can only focus your eye at infinity) at light from a mercury strip light or energy saving bulb (or sodium street lamp if it is dark enough) reflected off a sheet of white paper then you will see a set of circular fringes centred on your iris that do not alter in diameter which every part of the aperture you look through.

Should the fringes vary in diameter and open or close as you look through different parts of the aperture, then the parallelism is poor, and the etalon is either a bad example or broken.

[Merlin66]

Hmmmm

A very basic test...I'd be very surprised to see any of the current commercial etalons fail.

It's not a easy judgement to make, but when you image/ observe the solar surface you should be able to judge the bandwidth of the etalon.

A single etalon is usually capable of achieving 0.7A - this will show not only the obvious proms, but detail in the active areas and filaments.