ERF Prefilter - Energy Rejection Filter

BelOptik ERF energy rejection filters are protection prefilters for significantly reduce the heat and radiation power at the telescope focus. They are used primarily in connection with an H-alpha filter system.


  • H-alpha bandpass interference filter
  • FWHM 50nm @656.28nm
  • Schott glasses RG630 longpass
  • IR block coating 680nm - 1450nm
  • T ~90%
  • Thickness 5.3mm
  • Diffraction limited imaging
  • Diameter 105mm or 125mm
  • Aluminium filter cell optional

ERF 105mm... 449,-EUR (sold out)
ERF 125mm... 649,-EUR (sold out)
Filter cell...from 179,-EUR

In future I plan new designed dual band pass ERF's for CaK+H and H-alpha.

Follow images shows an old triple band pass ERF design incl. continuum light.