field distortion check

Robin Leadbeater

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