Narrow bandpass filters for emission lines in the night sky such as H-alpha, SII, H-beta, or OIII are basic and necessary for most of telescopes.
Recently narrow bandpass filters for galaxy redshift survey (e.g. redshifted H-alpha emission) have been required by many science groups.
Narrow bandpass filter that meets the following performances will contribute to your survey and science.
a. Small error for the target CWL and FWHM
b. Rectangular shape of passband
c. High transmission in passband
Actual transmission curve of past narrow bandpass filter was often significantly different from the theoretical design, and made astronomers disappointed.
However, Asahi is now successful to improve the gap between ideal and reality.