{"product_id":"sky-watcher-0-77x-reducer-flattener-for-esprit-150ed","title":"Sky-Watcher 0.77x Reducer\/Flattener for Esprit 150ED","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThe Esprit 150ED Reducer\/Flattener is Sky-Watcher's 0.77x corrector for the Esprit 150ED. It flattens the curved focal surface the triplet objective produces, so stars stay round out to the corners, and shortens the system at the same time. Sky-Watcher publishes the change as a drop from native f\/7 (1050mm) to f\/5.4 (810mm).\u003c\/p\u003e\n\u003cp\u003eOn the largest tube in the Esprit line, that shift matters most in time. Sky-Watcher publishes a 68% reduction in exposure time compared with native f\/7 — a 1050 mm f\/7 system is a demanding place to collect photons, and f\/5.4 turns the same target into a materially shorter project.\u003c\/p\u003e\n\u003cp\u003eThe frame widens with the reduction. Sky-Watcher publishes a 2.54 x 1.7-degree field of view on a full-frame camera and 1.66 x 1.11 degrees on APS-C, backed by a 36 mm fully illuminated field the vendor states is compatible with both APS-C and full frame sensors.\u003c\/p\u003e\n\u003cp\u003eThis is the reducing corrector for the Esprit 150ED. The Esprit 150EDX Flattener (S20219) is a separate part that flattens at native focal length and publishes no reduction.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is for Esprit 150ED owners who want the tube's aperture without its native 1050 mm framing — large emission nebulae, extended cluster fields, bright galaxy groups, anything that crowds the edges at f\/7. At 810 mm and f\/5.4 the same telescope covers 2.54 x 1.7 degrees on a full-frame sensor.\u003c\/p\u003e\n\u003cp\u003eIt also fits anyone whose clear nights are the scarce resource. The published 68% exposure reduction against native f\/7 is the difference between finishing a narrowband target over a season and finishing it over a few weeks.\u003c\/p\u003e\n\u003cp\u003eIf maximum image scale on small targets is the aim instead, a flattener working at the native 1050 mm is the part for that.\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\u003e0.77x reduction, published end to end:\u003c\/strong\u003e Sky-Watcher states the result as f\/7 (1050mm) dropping to f\/5.4 (810mm) on the Esprit 150ED, so both working figures come from the vendor.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReducer and flattener in one optic:\u003c\/strong\u003e curvature correction and focal reduction in a single unit, adding one element to the imaging train.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e36 mm fully illuminated field:\u003c\/strong\u003e Sky-Watcher's published figure, stated as compatible with both APS-C and full frame sensors.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTwo backfocus configurations:\u003c\/strong\u003e 90 mm back-focus as supplied, or 55 mm with the back focus spacer and M48 ring installed — 55 mm being the spacing most cooled astro cameras are built around.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBuilt-in 2\" filter cell:\u003c\/strong\u003e a 2-inch filter mounts into the light path inside the corrector rather than in a separate drawer.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eComplete in the box:\u003c\/strong\u003e Sky-Watcher lists the reducer, metal thread-on caps, back focus spacer and M48 thread adapter as included.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eOptical \/ Mechanical Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eWhat it corrects:\u003c\/strong\u003e field curvature across the Esprit 150ED imaging field, combined with a 0.77x focal reduction. Uncorrected, the corners of a large sensor show stars stretched radially while the frame centre is sharp; this optic flattens that surface onto the sensor plane and shortens the system in the same pass.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eResulting focal length and focal ratio:\u003c\/strong\u003e Sky-Watcher publishes the change as native f\/7 (1050mm) to f\/5.4 (810mm), stated for the Esprit 150ED specifically.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrected image circle:\u003c\/strong\u003e 36 mm fully illuminated, which the vendor states is compatible with both APS-C and full frame sensors. An APS-C sensor's roughly 28 mm diagonal sits inside the fully illuminated circle; a full-frame sensor spans 43.3 mm, so its extreme corners fall outside the 36 mm figure in the region Sky-Watcher covers with the full-frame compatibility statement. The published fields follow — 2.54 x 1.7 degrees full frame, 1.66 x 1.11 degrees APS-C.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eRequired backfocus:\u003c\/strong\u003e 90 mm as supplied, or 55 mm with the back focus spacer and M48 ring installed. 55 mm is the distance most cooled astronomical cameras and filter wheels are dimensioned to, so that is where most imaging trains settle.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eThread interface:\u003c\/strong\u003e M48, via the included M48 thread adapter that pairs with the 55 mm back focus configuration.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eFilter mounting:\u003c\/strong\u003e the built-in 2\" filter cell holds a 2-inch filter in the light path without adding a drawer or extra spacers to the train.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eWide-field deep-sky astrophotography:\u003c\/strong\u003e large emission and reflection nebulae, extended cluster fields and galaxy groups that run past the frame at 1050 mm.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNarrowband imaging:\u003c\/strong\u003e the faster f\/5.4 ratio offsets the transmission cost of narrow filters, and the built-in 2\" cell carries the filter in the light path.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLimited clear-sky sites:\u003c\/strong\u003e the published 68% exposure reduction against native f\/7 puts more finished signal into each usable night.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFull-frame and APS-C imaging:\u003c\/strong\u003e the 36 mm fully illuminated field is published as compatible with both, at 2.54 x 1.7 and 1.66 x 1.11 degrees respectively.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eSky-Watcher publishes this corrector for the Esprit 150ED, and the f\/7 (1050mm) to f\/5.4 (810mm) figures are stated for that telescope. Other Esprit models pair with their own correctors — including the separate Esprit 150EDX Flattener — and refractors from other makers have theirs. Send us the exact model printed on your tube and we will confirm which corrector belongs on it.\u003c\/p\u003e\n\u003cp\u003eThe box covers most of the spacing work: reducer, metal thread-on caps, back focus spacer and M48 thread adapter are all included. With the spacer and M48 adapter fitted, the corrector presents 55 mm of back focus, which is what a typical cooled camera plus filter wheel is built to consume. As supplied without them, it presents 90 mm, and that distance is filled by whatever sits between corrector and sensor.\u003c\/p\u003e\n\u003cp\u003eSend us your camera, filter wheel or drawer, off-axis guider and adapters and we will add the imaging train up with you and confirm which of the two configurations your setup wants. Filters thread into the built-in 2\" cell; cameras with an internal filter wheel simply leave that cell empty.\u003c\/p\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\u003eThe published figures are for the Esprit 150ED.\u003c\/strong\u003e 1050mm to 810mm and f\/7 to f\/5.4 are stated for that telescope. Other refractors reduce by their own numbers with their own correctors.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBackfocus sets corner star shape.\u003c\/strong\u003e The corrector presents 90 mm as supplied and 55 mm with the back focus spacer and M48 ring installed; the rest of the train is built to whichever figure you use.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e36 mm is the fully illuminated field.\u003c\/strong\u003e Sky-Watcher states compatibility with both APS-C and full frame sensors, with a full-frame sensor's outer corners lying beyond the 36 mm fully illuminated circle.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilter cell takes 2-inch filters.\u003c\/strong\u003e The built-in cell is sized for 2\" filters; other filter sizes go elsewhere in the train.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThis is the reducing corrector, not the flattener.\u003c\/strong\u003e The Esprit 150EDX Flattener is a separate part working at native focal length.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eVendor publishes no barcode for this SKU.\u003c\/strong\u003e The UPC we carry is 050234202152.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eVendor lists 2.0 lb for this item.\u003c\/strong\u003e That is the published weight; no separate optic-only mass appears in a specification table.\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 reducer threads into the imaging train once and stays there, and the parts that set the spacing — the back focus spacer and the M48 thread adapter — come in the box. The one decision is which backfocus you build to, 90 mm or 55 mm, and then adding camera, filter wheel and adapters up to that figure. Send us your components and we will do that arithmetic with you.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat focal length and focal ratio do I end up with?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eSky-Watcher publishes the Esprit 150ED as dropping from native f\/7 (1050mm) to f\/5.4 (810mm) with this reducer\/flattener fitted.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eHow much time does it save?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eSky-Watcher publishes a 68% reduction in exposure time compared with native f\/7.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it cover a full-frame sensor?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eSky-Watcher publishes a 36 mm fully illuminated field described as compatible with both APS-C and full frame sensors, quoting 2.54 x 1.7 degrees on a full-frame camera and 1.66 x 1.11 degrees on APS-C.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat comes in the box?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eSky-Watcher lists the reducer, metal thread-on caps, back focus spacer and M48 thread adapter.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I use filters with it?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes — a built-in 2\" filter cell mounts filters into the light path, so a 2-inch filter needs no separate drawer.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eSky-Watcher's own 0.77x corrector for the Esprit 150ED: f\/7 (1050mm) becomes f\/5.4 (810mm), exposure time drops by a published 68%, the frame opens to 2.54 x 1.7 degrees on full frame, and the back focus spacer, M48 adapter and thread-on caps are in the box. Tell us what camera and filters you run and we will confirm the 55 mm or 90 mm spacing with you before it ships.\u003c\/p\u003e","brand":"Sky-Watcher","offers":[{"title":"Default Title","offer_id":53896779858031,"sku":"S20215","price":730.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/S20215_Esprit150_RedFlat_web.jpg?v=1785253906","url":"https:\/\/ontariotelescope.com\/products\/sky-watcher-0-77x-reducer-flattener-for-esprit-150ed","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}