D-ERF energy protection filter 90 mm (5.0 mm thick / Ø 89.9 mm ± 0.05 mm)
D-ERF pre-filter for heat reduction for H-alpha observation with
SolarSpectrum Surface Filters and Prominence Approaches with IR
Block coating
Plane-parallel disc (WITHOUT socket) made of BK-7 glass, both surfaces are
Fine-optically polished to lambda/10.
IR-cut, dielectric coated