Here's another one Paul.
Well, to resolve my dispersion confusion I made a mosaic of the Fraunhofer C, D, E and G captures (F wasn't needed - it was all overlap) in IRIS, and then processed the lot together in VSpec.
Turns out the dispersion is 0.72 A/pixel, and at the same time I made a response curve for the ST8I and corrected the whole thing.
Its a pity VSpec won't let me stretch the spectrum wider, but I can always produce larger scale spectra if required.
Al.