IR pass filter 2″ – for astrophotography.
The IR pass filter (substrate thickness 2mm) blocks almost all of it
visible light off. At 685 nanometers (beyond the red light)
it has 50% transmission and the transmission curve rises steeply.
The cutoff starts very steeply at 685 nanometers, so you can
just focus and see a deep red image. That
The human eye is hardly sensitive in this area, that’s why
This filter is intended purely for photographic applications.