John,
Thanks!
The SHG is proving very stable. Once it's set up say, for H alpha, and you know the "best" focus setting.
It's just a matter of doing the scan.
The software is continually improving (Doug and Matt need congratulations and recognition for the upgrades they have done). Now you can select a pixel offset to the central wavelength and effectively scan the solar disk from the blue wing to the red wing in one pass.
You can't easily do that with an etalon filter!!!
I've put a copy of an excellent GIF by Pascal Berteau in my Dropbox (2Mb)
https://www.dropbox.com/s/j3bxq9mrh9...image.gif?dl=0