Terry / Al,
the attached pdf, (hope you can read it OK) were instructions given to me by Robin Leadbetter on how to process spectra, and get a camera response curve. It may be going over old ground, but I thought it may help. Certainly helped me!
Another comment from Robin was on the use of a focal reducer to improve the image. The aim was to get the smallest size zero order image, (basically increase FOV) and prevent significant focus shift and also smearing across the spectra. I've been using a 120mm f8 refractor and I get far better spectra when I use a 0.6x reducer and drop it to f5.
The exposure times are virtually unaffected.
cheers
Mark