Diffraction gratings
Resolutions of Common Diffraction Grating Films:
CD: 625 lines/mm SADGF: 1000 lines/mm (Simple Astronomical Diffaction Grating Film) DVD: 1350 lines/mm Blu-Ray: 3125 lines/mm HCF: 200-4000 lines/mm (Holographic Coating Film)
Higher lines/mm do NOT always help making a better spectrometer.