{"product_id":"farpoint-primary-mirror-center-marking-kit-large","title":"Farpoint Primary Mirror Center Marking Kit LARGE — 12\" to 26\"","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThe Farpoint Primary Mirror Center Marking Kit LARGE marks the exact centre of a big Newtonian or Dobsonian primary — mirrors from 12\" to 26\" in diameter. It contains a large precision-cut acetate template scaled for those apertures, together with eight triangle-shaped centre-mark targets.\u003c\/p\u003e\n\u003cp\u003eThe centre mark is what every collimation tool references. A laser reads where its beam returns relative to it, a Cheshire lines up reflected apertures around it, and an autocollimator stacks reflections of it. The triangle targets are cut so their edges meet the outside of the illuminated field seen through a Cheshire, which turns a judgement about centring into a straightforward read.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is a good match if you own a large Dobsonian or Newtonian — a 12\" to 26\" solid-tube, truss or collapsible scope — with an unmarked primary, a mark that has lifted or faded, or a mirror that has just come back from recoating. It is equally the kit for a mirror maker finishing a large primary, and for anyone assembling a truss Dob from components.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eLarge precision-cut acetate template:\u003c\/strong\u003e scaled for primary mirrors from 12\" to 26\", so the centre is located geometrically rather than measured across a large, awkward surface.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEight triangle centre-mark targets:\u003c\/strong\u003e enough for the job, a second attempt, and spares.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTriangular geometry:\u003c\/strong\u003e the edges meet the outside of the illuminated field through a Cheshire, which makes the alignment readable instead of estimated.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUniversal reference:\u003c\/strong\u003e works with laser collimators, Cheshire eyepieces and autocollimators of any make.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOne-time job:\u003c\/strong\u003e the mark stays put until the mirror is next recoated.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eWhy Centring Accuracy Scales With Aperture\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eCollimation brings the optical axes of the primary, the secondary and the focuser into agreement, and every tool that does it compares something against the centre of the primary. Without a mark there is no reference at all — the tools still show you a picture, but there is nothing in it to align to.\u003c\/p\u003e\n\u003cp\u003eOn a large mirror the accuracy of that mark matters more, not less. Big primaries generally come with fast focal ratios, and a fast Newtonian has a tighter tolerance for primary tilt than a slow one, so a given placement error translates into a larger optical consequence. The error is also self-concealing: because the laser, the Cheshire and the autocollimator all reference the same mark, an off-centre spot biases every adjustment by the same amount and none of the tools will contradict it. That is why the kit uses a cut template scaled to the aperture rather than leaving you to find the centre of a 20\" disc with a ruler.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eMarking a large unmarked primary:\u003c\/strong\u003e including mirrors bought separately or supplied unmarked with a truss kit.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAfter a recoat:\u003c\/strong\u003e recoating removes the old mark, and the mirror needs a new one before it can be collimated.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReplacing a lifted or inaccurate mark:\u003c\/strong\u003e worth redoing on a big mirror, where the consequences scale.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTruss and collapsible Dob assembly:\u003c\/strong\u003e the reference point for the alignment routine you will use every night out.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eATM and mirror-making projects:\u003c\/strong\u003e a finished large primary needs marking before first light.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eMirror size:\u003c\/strong\u003e Newtonian and Dobsonian primary mirrors from 12\" to 26\" in diameter.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSmaller mirrors:\u003c\/strong\u003e up to 12.5\", the standard Farpoint Primary Mirror Center Marking Kit is the correct template, and we stock it. The two overlap between 12\" and 12.5\".\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTelescope types:\u003c\/strong\u003e reflectors only. SCTs, Maksutovs, refractors and other catadioptric designs do not use a primary centre mark.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWorks with:\u003c\/strong\u003e Farpoint laser collimators, Cheshire eyepieces and autocollimators, and collimation tools of any other make.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNot the template supplied with Farpoint kits:\u003c\/strong\u003e Farpoint's lasers and collimation kits include the standard template for mirrors up to 12.5\". If your mirror is larger, this is the one you need.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eGood to Know Before You Order\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eCheck your mirror diameter.\u003c\/strong\u003e This template covers 12\" to 26\". Below 12\", the standard kit is the right size and we carry it.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReflectors only.\u003c\/strong\u003e A primary centre mark is a Newtonian and Dobsonian technique — SCTs, Maksutovs and refractors collimate differently. Tell us what you have and we will point you at the right approach.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt marks the mirror; it does not collimate it.\u003c\/strong\u003e The mark is the reference a laser, Cheshire or autocollimator then aligns to, so it is the first purchase rather than the only one.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eA large primary is heavy and awkward to handle.\u003c\/strong\u003e Marking means removing it from the mirror cell, so it is worth clearing a large padded surface and, on the biggest apertures, having a second pair of hands.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTake your time on placement.\u003c\/strong\u003e Eight targets are supplied precisely because the first attempt does not have to be the final one.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eFrequently Asked Questions\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eIs it difficult to set up?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe marking itself is simple — the template locates the centre and a triangle target goes on it. What takes care on a large scope is the handling: the primary comes out of its cell, and a 16\" or 20\" mirror wants a cleared, padded surface and an unhurried hour. Eight targets are supplied so a first attempt you are not satisfied with costs nothing, and Farpoint publishes preparation guides and downloadable collimation references if you would like to read the sequence through beforehand.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhy does the centre mark matter so much on a big mirror?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eLarge primaries usually come with fast focal ratios, and a fast Newtonian has a tighter tolerance for primary tilt. A placement error therefore has a larger optical consequence — and because every tool references the same mark, the error stays consistent and invisible rather than showing up as a disagreement between tools.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhy triangles rather than a round dot?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eA triangle gives you edges to read against. The edges meet the outside of the illuminated field through a Cheshire, so you match straight lines to a boundary rather than judging whether one circle sits centred inside another.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat size mirrors does this fit?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003ePrimary mirrors from 12\" to 26\" in diameter. Under 12\", the standard Farpoint center-marking kit is the correct template.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes the mark affect the view?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. The centre of the primary sits in the shadow of the secondary mirror, so that area contributes nothing to the image either way.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs this the template that comes with Farpoint's collimation kits?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo — those include the standard template for mirrors up to 12.5\". This LARGE version is the separate purchase for bigger apertures.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eIn short: a large precision-cut acetate template and eight triangle centre-mark targets for Newtonian and Dobsonian primaries from 12\" to 26\". It gives every other collimation tool a reference to work from, and on a big fast mirror it is the step the rest of the alignment rests on.\u003c\/p\u003e","brand":"Farpoint","offers":[{"title":"Default Title","offer_id":54271584403567,"sku":"FP208LG","price":42.99,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/LCKit_2IN_b7e1202e-1881-471c-99dc-f010db85eeb3.jpg?v=1789136842","url":"https:\/\/ontariotelescope.com\/products\/farpoint-primary-mirror-center-marking-kit-large","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}