Hi Derek,
A neat idea. You could use it to check how constant the dispersion is across the field. (A potential issue with objective gratings and wide angle lenses due to distortions)
Does anyone know if the wavelength is stable for a given pointer? (If so its wavelength could be calibrated) or does it vary eg with current and temperature? I have some cheap red green blue pointers. I might run some stability tests using the ALPY or LHIRES
Cheers
Robin