{"product_id":"takahashi-1-25-inch-multicoated-prism-star-diagonal","title":"Takahashi 1.25\" Multicoated Prism Star Diagonal","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eA 1.25-inch star diagonal built to Takahashi's mechanical standard, using a prism rather than a mirror. It takes a 1.25-inch male barrel into your focuser and presents a 1.25-inch female barrel with a clamp ring for the eyepiece, bending the light path 90° so you look down into a telescope pointed up.\u003c\/p\u003e\u003cp\u003eThe optical path through it measures 63.5 mm — the figure your focuser needs to accommodate, and the one to use when you are calculating whether an eyepiece will still reach focus. It weighs 135 g and measures 60 x 43 x 40 mm.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThis is the part that makes visual observing comfortable. Without a diagonal, a refractor pointed near the zenith puts the eyepiece near the ground. With one, you look down at a natural angle.\u003c\/p\u003e\u003cp\u003eIt suits refractors, Schmidt-Cassegrains and Maksutovs — anything with a 1.25-inch focuser or a visual back that accepts a 1.25-inch barrel. If you are already using Takahashi eyepieces, the mechanical fit is exact.\u003c\/p\u003e\u003cp\u003eIt is a visual component. Imaging trains connect a camera straight through and do not use a diagonal.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrism, not a mirror:\u003c\/strong\u003e total internal reflection at the prism face, so there is no reflective coating to age, tarnish or degrade.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMulticoated surfaces:\u003c\/strong\u003e applied to the entry and exit faces to cut reflection losses and internal ghosting.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNon-marring compression ring:\u003c\/strong\u003e clamps the eyepiece barrel evenly instead of driving a set screw into it, so barrels stay unmarked and the eyepiece sits square.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e1.25-inch male in, 1.25-inch female out:\u003c\/strong\u003e standard 31.75 mm fittings on both sides.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e63.5 mm metal backfocus length:\u003c\/strong\u003e the optical path the diagonal adds to your train.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e60 x 43 x 40 mm, 135 g:\u003c\/strong\u003e compact enough that focuser balance barely changes.\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003eFive-year manufacturer warranty.\u003c\/strong\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eOptical Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eA prism diagonal turns the light path using total internal reflection at the hypotenuse face of a glass prism, rather than bouncing it off an aluminised mirror surface. Total internal reflection is a property of the glass-air boundary itself, so nothing is lost to coating efficiency and nothing degrades with age — an aluminised mirror slowly dulls, a prism does not.\u003c\/p\u003e\u003cp\u003eThe trade is that light passes through glass, so the entry and exit faces are multicoated to hold down surface reflections and the scatter that would otherwise reduce contrast on planetary detail. At f\/6 and slower, which covers most of the Takahashi refractor range in visual use, a prism of this quality introduces no aberration that the eye can separate from the telescope's own.\u003c\/p\u003e\u003cp\u003eThe compression ring is the mechanical half of the design. A single set screw pushes an eyepiece barrel off-axis and leaves a dimple; the ring here spreads the clamping force around the barrel, which keeps the eyepiece square to the optical axis and the barrel unmarked.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eVisual observing with a refractor\u003c\/strong\u003e — lunar detail, planets, double stars, open clusters at a comfortable viewing angle.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSchmidt-Cassegrain and Maksutov visual backs\u003c\/strong\u003e that accept a 1.25-inch barrel.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eZenith observing\u003c\/strong\u003e, where a straight-through eyepiece position would be unusable.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTerrestrial and daytime use\u003c\/strong\u003e with a spotting eyepiece, noting that a star diagonal gives a mirror-reversed image.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eFocuser side:\u003c\/strong\u003e 1.25-inch (31.75 mm) male barrel — fits any 1.25-inch focuser or visual back directly.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEyepiece side:\u003c\/strong\u003e 1.25-inch (31.75 mm) female with clamp ring, so any 1.25-inch eyepiece seats in it.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOptical path:\u003c\/strong\u003e 63.5 mm. Add this to your train when checking that an eyepiece reaches focus — short-focus refractors with limited inward travel are where it matters.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e2-inch focusers:\u003c\/strong\u003e use a 2-inch to 1.25-inch reducing adapter, or move to a 2-inch diagonal if you plan to use 2-inch eyepieces. We stock both.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTakahashi visual adapters:\u003c\/strong\u003e the FS-60CB and the FC\/FS range each have a matching visual adapter that presents the correct barrel to this diagonal. Ask us which one your tube takes.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eImage orientation:\u003c\/strong\u003e a star diagonal produces a right-side-up but mirror-reversed image. That is normal for astronomical use; for terrestrial viewing an erecting prism gives a correctly oriented image.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eGood to Know Before You Order\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt adds 63.5 mm to the optical path.\u003c\/strong\u003e Most refractors have ample travel for that, and Takahashi publishes a backfocus table — included in the Downloads tab — covering the range if you want to check before ordering.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e1.25-inch only.\u003c\/strong\u003e It will not take 2-inch eyepieces. If you own or plan to own 2-inch wide-field eyepieces, a 2-inch diagonal is the better starting point.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThis is a visual component.\u003c\/strong\u003e Camera trains connect straight through and do not use a diagonal.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThe view is mirror-reversed.\u003c\/strong\u003e Standard for astronomical diagonals and of no consequence at the eyepiece; worth knowing if you also plan to use the telescope for daytime viewing.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePublished weight differs between Takahashi sources\u003c\/strong\u003e — 135 g on the European specification sheet, 3 oz (85 g) in the North American listing. Either way it is light enough not to affect focuser balance.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eFrequently Asked Questions\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eIs it difficult to set up?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eNo. The barrel slides into your focuser, the eyepiece goes into the clamp ring, and the ring tightens by hand. There is nothing to align or adjust.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003ePrism or mirror — which is better?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eA prism uses total internal reflection, so there is no coating to degrade over the years, and it tends to hold contrast well on planetary detail at moderate focal ratios. Mirror diagonals are usually preferred at very fast focal ratios and in 2-inch formats. For visual work on a Takahashi refractor, a prism of this quality is a sound match.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it fit my telescope?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eIt fits any 1.25-inch focuser or visual back directly. On a 2-inch focuser you need a reducing adapter; on a Takahashi tube with a proprietary rear thread you need the matching visual adapter. Tell us your telescope and we will confirm the part.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill my eyepieces still reach focus?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eThe diagonal adds 63.5 mm of optical path. Most refractors have enough travel to absorb it. The Takahashi backfocus table below covers the range, and we are happy to check a specific combination for you.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it for astrophotography?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eNo — imaging trains connect the camera directly to the corrector or telescope. This is for eyepiece observing.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it mark my eyepiece barrels?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eNo. The compression ring clamps evenly around the barrel rather than pressing a screw point into it.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is in the box?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eThe diagonal itself. Eyepieces and any focuser adapters are separate.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eIn short: a 135 g multicoated prism diagonal that adds 63.5 mm to a 1.25-inch visual train, clamps eyepieces without marking them, and has no reflective coating to age. It is the piece that makes a refractor comfortable to observe with.\u003c\/p\u003e","brand":"Takahashi","offers":[{"title":"Default Title","offer_id":54046969888879,"sku":"TAK-TKA00547","price":167.31,"currency_code":"CAD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/TKA00547_1.jpg?v=1786907778","url":"https:\/\/ontariotelescope.com\/products\/takahashi-1-25-inch-multicoated-prism-star-diagonal","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}