Daystar Energy Rejection Filters reduce the heat load on your filter assembly by absorbing or reflecting UV and/or IR light and transmitting light in the desired visual spectrum. These filters are sometimes Red or Yellow glass, or dielectric IR and UV, but pass light in the desired visual spectrum.  

The ERF also serves as an aperture mask to accomplish a straight angle of incidence for light entering the filter. This raises the focal ratio of your scope for the Quark etalon to work best.

This ERF has a 63mm glass filter set into a 244mm cap that suits 8″ Schmidt-Cassegrain telescopes.

When ordering, please ensure you have the correct diameter of your telescope’s dew shield (at the very front of the telescope).  ERFs are custom machined on a one-off basis and so the accuracy of this measurement is very important. If you are in doubt, contact Sidereal Trading – we are able to get a wide range of sizes.