Peter,
Thanks for the interest in the digital SHG.
The best resource is my book "Imaging Sunlight - Using the Digital Spectroheliograph" available on Amazon etc. (I also have signed copies available)
This gives all the technical details, examples of the SHG from around the world and reviews all the processing software currently available.
Fulvio's page is worth reading:
http://www.lightfrominfinity.org/
I translated Daniel's page into english:
http://www.astrosurf.com/cieldelabrie/sphelio.en.htm
Basically the Digital SHG is a telescope fitted with a spectrograph and a fast frame camera. I use an ASI 174mm and ASI 1600mm, Firecapture to acquire the solar spectral image (running to an MSI laptop, USB3, SSD drive). I can scan the solar disk in 20sec using 90 fps, giving a 1.7 Gb AVI/ SER file.
My Sim Spec SHG spreadsheet allows the calculation of the solar image size, spectral dispersion and probable resolution.
The spectral image is cropped (using VDub) then processed to an image using Wah! "Spectral Line Merge" or BASS Project.
The attached illustrations show the spectral line and the constructed image, the series of AVI images during the scan and an excellent solar disk image (not mine!)
Hope this helps. If you need any further info, drop me an email