Daystar ERF 130mm with 180mm Cap - E-180N130

130mm ERF Glass, Cell & 180mm ID Cap - For RefractorsDayStar 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. Higher resolution, larger aperture configurations use a barlow.***This is a research-grade product that is made-to-order in the United States. Currently, this product has a 4-6 week delivery wait. Please contact us to confirm lead time.In the order notes, please specify the telescope this ERF is to be used with, and measure (with a ruler) the outside (largest) diameter of your telesc