What is the Peak Transmission of the Filter?
This peak transmission of the filter is a very important parameter. It represents how much light passes through the filter. This is expressed in percent, such as 95%T (T=transmittance or transmission). This means at that wavelength, the filter passes 95 out of every 100 photons to the detector. Commercial (non-astronomy) filters typically transmit only 50-60%. Astronomy is much more demanding, and nowadays, narrowband astronomy filters transmit in excess of 80%. The transmission of the filter improves the signal in the signal-to-noise (S/N) of your image. So, you want this value as high as possible. Astrodon 5 nm narrowband filters typically have 95%T, the highest value available, for this reason. Even our ultra-narrow 3 nm filters are guaranteed to be >90%T.
