As the light encounters 18 glass/air interfaces, a total loss of less than 2% requires an AR coating providing < 0.12% loss. This is not impossible to achieve: Melles Griot specifies 0.25% for their V-coatings but states that 0.1% is often achieved.

Note:

1. Wavelength spec is 495 < 507 ([OIII])
2. Wavelength spec is 648.8 < 664.5 (Halpha, Halpha/[OIII] is 1.311)
3. The performance is dependent on maximum angle of incidence and we should specify this
4. 502nm is a standard wavelength for Melles Griot

AR coating collimator

AR coating [OIII] cameras

AR coating Halpha camera

Substrate and coating for dichroic