{"product_id":"filtro-d-erf-baader-110mm-energy-rejection","title":"Baader D-ERF Filter 110mm Energy Rejection Anti-IR","description":"\u003cp\u003e\u003cstrong\u003eThe Baader D-ERF 110mm filter\u003c\/strong\u003e is an infrared pre-filter mounted in front of the telescope objective, essential for H-alpha solar observation with Solar Spectrum filters: it reduces the thermal load, protects the etalon and stabilizes the band wavelength.\u003c\/p\u003e\n\n\u003ch2\u003eWhat the D-ERF is for\u003c\/h2\u003e\n\u003cp\u003eAn ERF (Energy Rejection Filter) blocks most of the solar energy before it enters the optical tube, preventing overheating of the H-alpha etalon and the telescope optics — a particularly relevant issue on SCT\/Mak catadioptrics, where internal heat causes image turbulence. The result is a \"cold\" focus, longer H-alpha filter life, and no internal air currents in the tube.\u003c\/p\u003e\n\n\u003ch2\u003eHigh-precision BK7 optical glass\u003c\/h2\u003e\n\u003cp\u003eUnlike older red-glass ERFs, prone to internal defects, the D-ERF is made of high-quality BK7 optical glass, plane-parallel worked and polished to 1\/10 wave across the entire surface.\u003c\/p\u003e\n\n\u003ch2\u003eMulti-layer dielectric coating\u003c\/h2\u003e\n\u003cp\u003eEnergy rejection is achieved through a highly resistant multi-layer dielectric coating on both glass surfaces, which also protects the surface from scratches.\u003c\/p\u003e\n\n\u003ch2\u003eTechnical specifications\u003c\/h2\u003e\n\u003ctable\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\u003ctd\u003eDiameter\u003c\/td\u003e\u003ctd\u003e110 mm\u003c\/td\u003e\u003c\/tr\u003e\n\u003ctr\u003e\u003ctd\u003eGlass thickness\u003c\/td\u003e\u003ctd\u003e8 mm\u003c\/td\u003e\u003c\/tr\u003e\n\u003ctr\u003e\u003ctd\u003eMaterial\u003c\/td\u003e\u003ctd\u003eBK7 optical glass\u003c\/td\u003e\u003c\/tr\u003e\n\u003ctr\u003e\u003ctd\u003eCoating\u003c\/td\u003e\u003ctd\u003eMulti-layer dielectric IR-Cut\u003c\/td\u003e\u003c\/tr\u003e\n\u003ctr\u003e\u003ctd\u003eHalf-Band-Width (HBW)\u003c\/td\u003e\u003ctd\u003e80 nm\u003c\/td\u003e\u003c\/tr\u003e\n\u003ctr\u003e\u003ctd\u003eSupplied as\u003c\/td\u003e\u003ctd\u003eUnmounted glass (no filter cell)\u003c\/td\u003e\u003c\/tr\u003e\n\u003ctr\u003e\u003ctd\u003eMade in\u003c\/td\u003e\u003ctd\u003eGermany\u003c\/td\u003e\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch2\u003eFrequently asked questions\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eDoes the D-ERF replace the H-alpha filter?\u003c\/strong\u003e No, it's a pre-filter: it must always be used together with a Solar Spectrum H-alpha filter, never alone.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs it suitable for direct visual observation of the Sun?\u003c\/strong\u003e No: without a downstream H-alpha filter, the D-ERF alone is not safe for visual observation.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes the filter include a mount?\u003c\/strong\u003e No, it is supplied as unmounted glass.\u003c\/p\u003e\n\n\u003ch2\u003e⚠️ Safety warning\u003c\/h2\u003e\n\u003cp\u003eThe D-ERF must \u003cstrong\u003ealways be mounted in front of\u003c\/strong\u003e the telescope aperture and used \u003cstrong\u003eexclusively together with a Solar Spectrum H-alpha filter\u003c\/strong\u003e. Improper use can cause severe, permanent eye damage.\u003c\/p\u003e","brand":"Baader-Planetarium","offers":[{"title":"Default","offer_id":57940705837387,"sku":"BRBP2459243D","price":560.0,"currency_code":"EUR","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0886\/1981\/1147\/files\/Baader-Filters-C-ERF-energy-guard-filter-110mm-IR-CUT-dielectrically-coats.jpg?v=1784960514","url":"https:\/\/adriasky.it\/en\/products\/baader-d-erf-filter-110mm-energy-rejection","provider":"Adriasky","version":"1.0","type":"link"}