Astronomy Specialist




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DayStar Energy Rejection Filters reduce the heat load on your filter assembly by absorbing or reflecting UV and/or I 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 can also serve as an aperture mask to accomplish a straight angle of incidence for light entering the filter.

DayStar filter assemblies operate best at f/30 and slower. Creating f/30 configuration can be done easily with the proper ERF and/or barlow.

In order to find the right ERF for your system, measure (with a ruler) the outside (largest) diameter of your telescope's dew shield at the very front of the telescope and size up to the nearest available ERF diameter (ie. for SkyWatcher Esprit 80 ED, the dew shield measures 125mm so you will need the 100 mm ERF for dew shields Ø 150 mm).


80 mm ERF for dew shields Ø 120 mm
100 mm ERF for dew shields Ø 150 mm DS-E-150N100
130 mm ERF for dew shields Ø 180 mm DS-E-180N130
150 mm ERF for dew shields Ø 220 mm DS-E-220N150



SkyWatcher Evostar 80 ED
115 mm
SkyWatcher Evostar 100 ED 115 mm
SkyWatcher Evostar 120 ED 140 mm
SkyWatcher Esprit 80 ED 125 mm
SkyWatcher Esprit 100 ED 150 mm
SkyWatcher Esprit 120 ED 165 mm
SkyWatcher Esprit 150 ED 202 mm
Sharpstar 61EDPH-II 92 mm
Sharpstar 76EDPH 100 mm
Sharpstar 94EDPH 122 mm
Sharpstar 100Q-II 134 mm
Sharpstar 121SDQ 160 mm
Sharpstar AL-140PH 179 mm
Askar FRA400 100 mm
Askar FRA600 148 mm
Explore Scientific ES-ED80 127 mm
Explore Scientific ES-ED102 153 mm
Explore Scientific ES-ED127 175 mm
Explore Scientific FCD100 102 145.5 mm
William Optics FLT 132 168 mm
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