{"product_id":"explore-scientific-3-inch-99-dielectric-star-diagonal","title":"Explore Scientific 3-inch 99% Dielectric Star Diagonal with 2-inch Adapter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 3-inch Dielectric-Coated Diagonal Mirror turns the light path 90 degrees for comfortable viewing on a refractor, and does so with a first-surface coated mirror that reflects 99% of the light reaching it. It ships with a 2-inch adapter and dust covers, and weighs 2.0 lb.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis is the diagonal for an observer running a large refractor with a 3-inch focuser who does not want the diagonal to be the narrowest point in the optical path. A 2-inch diagonal on a 3-inch focuser throws away field at the edges; this one passes the full aperture. It suits anyone using wide-field 2-inch eyepieces on a 120 mm or larger refractor.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e99% reflective dielectric coating on a first-surface mirror, preserving image brightness\u003c\/li\u003e\n\u003cli\u003eFull 3-inch clear path with no restriction ahead of the eyepiece\u003c\/li\u003e\n\u003cli\u003eDouble-taper insert barrel for smooth insertion and withdrawal from the focuser\u003c\/li\u003e\n\u003cli\u003eWide section of the taper prevents the diagonal dropping out if the focuser set screw loosens\u003c\/li\u003e\n\u003cli\u003eCompression ring lock on the 2-inch eyepiece holder, gripping without marking the barrel\u003c\/li\u003e\n\u003cli\u003e2-inch adapter and dust covers included\u003c\/li\u003e\n\u003cli\u003eSolid but light construction at 2.0 lb\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eOptical and Mechanical Design\u003c\/h2\u003e\u003cp\u003eA first-surface mirror carries its reflective coating on the front of the glass, so light never passes through the substrate — that removes the faint secondary reflection a rear-coated mirror produces around bright objects. The dielectric coating is a multi-layer stack tuned for reflectivity across the visual band rather than a metal film, which is what allows a 99% figure and why it does not tarnish with age. The double-taper barrel is a mechanical safety feature as much as a convenience: a heavy diagonal and eyepiece cannot slide free of a loosened set screw.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eVisual observing with a large refractor at a comfortable eyepiece angle\u003c\/li\u003e\n\u003cli\u003eWide-field views with 2-inch eyepieces where full aperture matters at the field edge\u003c\/li\u003e\n\u003cli\u003eLunar, planetary and double star work where every percent of light and contrast counts\u003c\/li\u003e\n\u003cli\u003eAny 3-inch focuser setup where a 2-inch diagonal would be the limiting aperture\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe diagonal is built for a 3-inch focuser such as the Explore Scientific ES-FOC3, and the supplied 2-inch adapter lets you use your existing 2-inch eyepieces straight away. A 1.25-inch eyepiece holder is available separately if you also want to use smaller barrels; it has its own compression ring lock. Both holders secure eyepieces with compression rings rather than a bare set screw, so eyepiece barrels stay unmarked. We stock 2-inch eyepieces across the Explore Scientific 68°, 82° and 92° series if you are building out a set.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eThis is a 3-inch diagonal — it needs a 3-inch focuser, and will not fit a 2-inch one. The 1.25-inch eyepiece holder is a separate purchase, so if most of your eyepieces are 1.25-inch it is worth adding. At 2.0 lb plus an eyepiece it is a real load on the focuser, which is part of why it pairs naturally with a heavy-duty 3-inch focuser rated for the weight. Not sure whether your focuser takes it? Send us the model and we will confirm.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eIs it difficult to set up?\u003c\/strong\u003e No. It slides into a 3-inch focuser and locks with the focuser's own mechanism; the eyepiece drops into the compression ring holder and tightens by hand.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill my 2-inch eyepieces work?\u003c\/strong\u003e Yes — the 2-inch adapter is included in the box.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat about 1.25-inch eyepieces?\u003c\/strong\u003e A 1.25-inch holder is available separately and adds a second compression ring lock.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy choose a 3-inch diagonal over a 2-inch?\u003c\/strong\u003e On a 3-inch focuser a 2-inch diagonal becomes the narrowest point in the light path and clips the outer field. A 3-inch diagonal keeps the full aperture through to the eyepiece.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eA 99% dielectric first-surface mirror in a full 3-inch body, with the 2-inch adapter and dust covers included and a barrel designed not to let go. The right diagonal for a large refractor running a 3-inch focuser. Our Bolton team can confirm fit and suggest eyepieces to match.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53956030201967,"sku":"DD03-01CF","price":817.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/DD03-01CF_1_55bf8ec6-c7ec-4584-b1a9-a36a2163be15.jpg?v=1785953832","url":"https:\/\/ontariotelescope.com\/products\/explore-scientific-3-inch-99-dielectric-star-diagonal","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}