{"product_id":"daystar-energy-rejection-filter-for-refractor-erf","title":"Daystar Energy Rejection Filter for Refractor- ERF","description":"\u003ch2\u003eDaystar Energy Rejection Filter ERF for Refractor\u003c\/h2\u003e\n\u003cp\u003e\u003cspan style=\"font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;\"\u003eThe Daystar Energy Rejection Filter for Refractor 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\u003c\/p\u003e\n\u003cdiv title=\"Page 1\" class=\"page\"\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\u003e\u003c\/h3\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. A refractor with an aperture of 80mm or less doesn't require energy rejection. This is because the amount of energy collected with 80mm of light just isn't enough to do damage to your system. 80mm is the size of the palm of your hand. Your hand doesn't spontaneously ignite in the sun - and it's not transparent like your refractor's objective is. All of your lenses are transparent and do not absorb energy.  A diagonal and the front elements of the QUARK are \u0026gt;99% reflective and doesn't either.  All of that energy is reflected back out the front of your telescope unmagnified.  Unless your telescope is made of paper, then it is not at-risk for damage with an aperture of 80mm or less.\u003c\/div\u003e\n\u003ch3\u003e\u003c\/h3\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$\\text{Useable Clear Aperture (ERF Size)}=\\frac{\\text{Scope Focal Length }\\times\\text{ Barlow Power}}{30}$\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\"\u003eERF\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":"80mm ERF Glass Cell \u0026 110mm ID Cap","offer_id":43666950455525,"sku":"DAY-E-110N80","price":770.0,"currency_code":"CAD","in_stock":true},{"title":"80mm ERF Glass Cell \u0026 120mm ID Cap","offer_id":43666950488293,"sku":"DAY-E-120N80","price":770.0,"currency_code":"CAD","in_stock":true},{"title":"100mm ERF Glass Cell \u0026 120mm ID Cap","offer_id":43666950521061,"sku":"DAY-E-120N100","price":973.0,"currency_code":"CAD","in_stock":true},{"title":"100mm ERF Glass Cell \u0026 130mm ID Cap","offer_id":43666950553829,"sku":"DAY-E-130N100","price":973.0,"currency_code":"CAD","in_stock":true},{"title":"100mm ERF Glass Cell \u0026 140mm ID Cap","offer_id":43666950586597,"sku":"DAY-E-140N100","price":973.0,"currency_code":"CAD","in_stock":true},{"title":"100mm ERF Glass Cell \u0026 150mm ID Cap","offer_id":43666950619365,"sku":"DAY-E-150N100","price":973.0,"currency_code":"CAD","in_stock":true},{"title":"130mm ERF Glass Cell \u0026 150mm ID Cap","offer_id":43666950652133,"sku":"DAY-E-150N130","price":1393.0,"currency_code":"CAD","in_stock":true},{"title":"130mm ERF Glass Cell \u0026 160mm ID Cap","offer_id":43666950684901,"sku":"DAY-E-160N130","price":1393.0,"currency_code":"CAD","in_stock":true},{"title":"130mm ERF Glass Cell \u0026 170mm ID Cap","offer_id":43666950717669,"sku":"DAY-E-170N130","price":1393.0,"currency_code":"CAD","in_stock":true},{"title":"130mm ERF Glass Cell \u0026 180mm ID Cap","offer_id":43666950750437,"sku":"DAY-E-180N130","price":1393.0,"currency_code":"CAD","in_stock":true},{"title":"130mm ERF Glass Cell \u0026 190mm ID Cap","offer_id":43666950783205,"sku":"DAY-E-190N130","price":1393.0,"currency_code":"CAD","in_stock":true},{"title":"150mm ERF Glass Cell \u0026 180mm ID Cap","offer_id":43666950881509,"sku":"DAY-E-180N150","price":2303.0,"currency_code":"CAD","in_stock":true},{"title":"150mm ERF Glass Cell \u0026 190mm ID Cap","offer_id":43666950914277,"sku":"DAY-E-190N150","price":2303.0,"currency_code":"CAD","in_stock":true},{"title":"150mm ERF Glass Cell \u0026 200mm ID Cap","offer_id":43666950947045,"sku":"DAY-E-200N150","price":2303.0,"currency_code":"CAD","in_stock":true},{"title":"150mm ERF Glass Cell \u0026 210mm ID Cap","offer_id":43666950979813,"sku":"DAY-E-210N150","price":2303.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0652\/6245\/2965\/files\/daystar-energy-rejection-filter-for-refractor-erf-astronomy-plus_96599091-76b0-412a-9e90-d92f9763657b.png?v=1690484514","url":"https:\/\/istronomyplus.com\/products\/daystar-energy-rejection-filter-for-refractor-erf","provider":"Astronomy Plus – Telescopes \u0026 Astrophotography Canada","version":"1.0","type":"link"}