{"product_id":"daystar-energy-rejection-filter-for-sct-erf","title":"Daystar Energy Rejection Filter for SCT- ERF","description":"[latexpage]\n\u003ch2\u003eDaystar Energy Rejection Filter ERF for SCT\u003c\/h2\u003e\n\u003cspan style=\"font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;\"\u003eThe Daystar Energy Rejection Filter for SCT reduces 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.\u003c\/span\u003e\n\u003cdiv class=\"page\" title=\"Page 1\"\u003e\n\u003cdiv class=\"layoutArea\"\u003e\n\u003cdiv class=\"column\"\u003eTo prevent damage, we recommend using an Energy Rejection Filter on telescopes of 80mm aperture or more, or when tracking the Sun for long periods. This can be a UV\/IR cut filter mounted before the diagonal, or a full aperture red or yellow glass ERF mounted in front of the telescope.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003ch3\u003eWhen to use a Front Mounted ERF\u003c\/h3\u003e\nTelescopes upon which we do not recommend UV\/IR cut filters:\n\u003cul\u003e\n\u003cli\u003eSome larger aperture (130mm and higher) and\/or all-day tracking applications where the Quark \/ Quantum are susceptible to overheating.\u003c\/li\u003e\n\u003cli\u003eSCT telescopes\u003c\/li\u003e\n\u003cli\u003ePetzval refractors (a concentrated beam will fall upon unknown coatings)\u003c\/li\u003e\n\u003cli\u003eCertain older oil spaced triplets prior to adoption of UV resistant oils.\u003c\/li\u003e\n\u003cli\u003eAny instrument for which the owner is not comfortable with the UV\/IR cut solution.\u003c\/li\u003e\n\u003c\/ul\u003e\nThese users should consider front mount energy rejection.  This is accomplished using a colored glass optical window before the objective or corrector plate.\u003c\/div\u003e\n\u003ch3\u003eWhich Front Mounted ERF Do I Need?\u003c\/h3\u003e\n\u003cspan style=\"font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;\"\u003eDayStar 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. \u003c\/span\u003e\n\u003cp style=\"text-align: center;\"\u003e$text{Useable Clear Aperture (ERF Size)}=frac{text{Scope Focal Length }timestext{ Barlow Power}}{30}$\u003c\/p\u003e\n\u003ch3\u003eHow it Works?\u003c\/h3\u003e\n\u003cp\u003eColored glass ERF's must maintain an optical figure. This means they must be somewhat thick and must be polished to 1\/4 wave accuracy. This factor drives the cost of front mount Energy Rejection Filters. Colored glass ERF's block all Ultraviolet light and all visible light below the 500nm range.  Red glass blocks all visible light below 600nm (making it red).  We choose Yellow 500nm cut point glass in the event that an owner might later acquire a Sodium or Helium D3 line filter.  The same glass can be used for both types of filters, but Red glass can only be used for Hydrogen. Colored glass front mount ERF filters do not pass Calcium 393nm light.  Calcium owners must use UV\/IR cut filters only or no viable image will pass. All front mount Energy Rejection Filters must be fabricated to fit the front dew shield of the telescope.  Due to the thousands of designs and modifications of telescopes over the decades, the owner must measure his\/her own dew shield to determine the best inside diameter size offered which fits best over his exact instrument. \u003cu\u003e\u003cem\u003e\u003cstrong\u003eIT MUST BE NOTED THAT A UV\/IR CUT FILTER, NOR A FRONT MOUNT COLORED GLASS FILTER IS NOT SUFFICIENT FILTRATION FOR SOLAR VIEWING ALONE.\u003c\/strong\u003e\u003c\/em\u003e\u003c\/u\u003e\u003c\/p\u003e\n\u003ch3 data-mce-fragment=\"1\"\u003eIn the Box\u003c\/h3\u003e\n\u003cul data-mce-fragment=\"1\"\u003e\n\u003cli data-mce-fragment=\"1\"\u003e\u003cspan mce-data-marked=\"1\"\u003eERF Filter\u003c\/span\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3 data-mce-fragment=\"1\"\u003eWarranty \u0026amp; Manuals\u003c\/h3\u003e\n\u003cp data-mce-fragment=\"1\"\u003eDaystar 1-Years Warranty\u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e","brand":"Daystar","offers":[{"title":"63mm ERF Glass (Off-Axis) Cell \u0026 244mm ID Cap","offer_id":43666980372709,"sku":"DAY-E-244F63","price":770.0,"currency_code":"CAD","in_stock":true},{"title":"80mm ERF Glass (Off-Axis) Cell \u0026 281mm ID Cap","offer_id":43666980405477,"sku":"DAY-E-281F80","price":770.0,"currency_code":"CAD","in_stock":true},{"title":"80mm ERF Glass (Off-Axis) Cell \u0026 311mm ID Cap","offer_id":43666980438245,"sku":"DAY-E-311F80","price":770.0,"currency_code":"CAD","in_stock":true},{"title":"90mm ERF Glass (Off-Axis) Cell \u0026 311mm ID Cap","offer_id":43666980471013,"sku":"DAY-E-325F90","price":973.0,"currency_code":"CAD","in_stock":true},{"title":"100mm ERF Glass (Off-Axis) Cell \u0026 356mm ID Cap","offer_id":43666980503781,"sku":"DAY-E-356F100","price":1253.0,"currency_code":"CAD","in_stock":true},{"title":"115mm ERF Glass (Off-Axis) Cell \u0026 410mm ID Cap","offer_id":43666980536549,"sku":"DAY-E-410F115","price":1673.0,"currency_code":"CAD","in_stock":true},{"title":"125mm ERF Glass (Off-Axis) Cell \u0026 460mm ID Cap","offer_id":43666980569317,"sku":"DAY-E-460F125","price":1673.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0652\/6245\/2965\/files\/daystar-energy-rejection-filter-for-sct-erf-astronomy-plus_b707b1e1-378f-4579-9ece-4ed4a1b2f20a.png?v=1690484513","url":"https:\/\/istronomyplus.com\/products\/daystar-energy-rejection-filter-for-sct-erf","provider":"Astronomy Plus – Telescopes \u0026 Astrophotography Canada","version":"1.0","type":"link"}