{"product_id":"idas-ol7-5-low-profile-filter-for-celestron-rasa-8","title":"IDAS OL7.5 Low-Profile Filter for Celestron RASA 8 (M42 \/ M54)","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eEngineered to consume exactly 7.5mm of optical path\u003c\/li\u003e\n\u003cli\u003eSolves the Celestron RASA 8 25.0mm backfocus requirement with 17.5mm cameras\u003c\/li\u003e\n\u003cli\u003eAvailable in M42 mount (37mm clear aperture) for APS-C sensors\u003c\/li\u003e\n\u003cli\u003eAvailable in M54 mount (47mm clear aperture) for full-frame and Duo cameras\u003c\/li\u003e\n\u003cli\u003e2.0mm thick IDAS filter glass, made in Japan\u003c\/li\u003e\n\u003cli\u003eOptional M42-M54 adapter adds 0mm to the optical path\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eDownloads\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eIDAS OL7.5 Low-Profile Filter for Celestron RASA 8 (M42 \/ M54)\u003c\/h2\u003e\n\u003cp\u003eThe IDAS OL7.5 Low-Profile Filter is a filter built into a precision frame made in Japan that consumes exactly 7.5mm of optical path. It matches the Celestron RASA 8's strict 25.0mm backfocus requirement when paired with a standard 17.5mm flange-back camera (7.5mm + 17.5mm = 25.0mm). Built with 2.0mm thick glass, it is available in an M42 mount with a 37mm clear aperture for APS-C sensors or an M54 mount with a 47mm clear aperture for full-frame coverage.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eThe 7.5mm Optical Path Solution for RASA 8\u003c\/h3\u003e\n\u003cp\u003eThe Celestron RASA 8 demands a precise 25.0mm backfocus distance from its M42 camera adapter to the sensor. Because the OL7.5 frame consumes exactly 7.5mm of optical path, it pairs with a standard cooled camera that has a 17.5mm flange back to give the exact 25.0mm reference backfocus.\u003c\/p\u003e\n\u003cp\u003eInstallation takes three steps:\u003c\/p\u003e\n\u003col\u003e\n\u003cli\u003eAttach the standard M42 camera adapter included with your RASA 8 (with the M54 version, first thread the M42-M54 adapter ring onto it).\u003c\/li\u003e\n\u003cli\u003eThread the IDAS OL7.5 filter onto the adapter.\u003c\/li\u003e\n\u003cli\u003eThread your 17.5mm flange-back cooled camera onto the filter. The total is exactly 25.0mm.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003e8.1mm Mechanical vs. 7.5mm Optical: How 2.0mm Glass Refraction Works\u003c\/h3\u003e\n\u003cp\u003eWhile the physical, flange-to-flange measurement of the OL7.5 filter holder is 8.1mm, its effect on your optical train is only 7.5mm. This difference is due to the refractive properties of the 2.0mm thick filter glass. The glass refracts light and pushes the focal plane back by about 0.6mm.\u003c\/p\u003e\n\u003cp\u003eIDAS designed the frame around this shift, so the net optical path consumption is exactly 7.5mm.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eM42 OL7.5 Mount: A 37mm Aperture for APS-C Sensors\u003c\/h3\u003e\n\u003cp\u003eThe M42 OL7.5 version is for APS-C and Four Thirds sensors. It has M42 x P0.75 threads on both sides (male camera side, female scope side) and a 37mm clear aperture, the largest possible within the M42 thread. This significantly reduces peripheral vignetting on APS-C and Four Thirds sensors. It mounts directly to M42 cooled cameras with a 17.5mm flange back, and adapts to M48 or M54 cameras with standard step-up rings (not included). For full-frame or Duo guiding cameras, IDAS recommends the M54 version.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eM54 OL7.5 Mount: A 47mm Aperture for Full-Frame \u0026amp; Duo Cameras\u003c\/h3\u003e\n\u003cp\u003eFor full-frame sensors and Duo cameras with a built-in guide sensor (such as the ZWO ASI2600MC Duo), choose the M54 OL7.5. It has M54 x P0.75 threads (male camera side, female scope side) and a 47mm clear aperture that accommodates the steep light cones of ultra-fast optics such as F\/2. Compared with M42 or M48 threads, it suppresses aperture clipping and significantly reduces peripheral vignetting on APS-C and full-frame sensors, and it prevents frame clipping on the outer guide sensor of Duo cameras.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eThe M42-M54 Adapter Option (0mm Optical Path)\u003c\/h3\u003e\n\u003cp\u003eTo use the M54 filter on telescopes that end in an M42 male thread, such as the RASA 8 with its standard M42 camera adapter, IDAS makes a dedicated M42-M54 adapter ring. It sits completely flush inside the filter's front threads, so it adds 0.0mm of optical backfocus and your 7.5mm + 17.5mm calculation stays the same.\u003c\/p\u003e\n\u003cp\u003eChoose \u003cstrong\u003eM54 OL7.5 + M42-M54 adapter\u003c\/strong\u003e for a RASA 8 with its standard M42 adapter, or if this is your first M54 OL7.5. Choose \u003cstrong\u003eM54 OL7.5\u003c\/strong\u003e alone if your telescope already ends in a native M54 male thread, or if you already own the adapter and are adding a second filter.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eChoosing Your IDAS Filter: From NBZ-II to Clear\u003c\/h3\u003e\n\u003cp\u003eEach filter also has its own IDAS product page on our store with its transmission curve and full details. NB1 and DTD come in the M42 mount only, and NBZ-II in the M54 mount only.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eNBZ-II:\u003c\/strong\u003e Dual-band H-alpha \/ OIII nebula booster.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDTD:\u003c\/strong\u003e Next-generation natural nightglow and light pollution cut color booster for comets, galaxies, the Milky Way and nebulae.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNGS1:\u003c\/strong\u003e Night glow suppression light pollution filter.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eGNB:\u003c\/strong\u003e Galaxy and nebula booster with a high near-infrared passband.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eHEUIB-II:\u003c\/strong\u003e H-alpha enhanced UV\/IR block filter.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNB1:\u003c\/strong\u003e Triple-band nebula booster (OIII, H-alpha, NII).\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eClear:\u003c\/strong\u003e Optical clear protection filter (ODW in the M54 mount).\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eA Note on F\/2 Optics: Sensor Tilt, Collimation, and Shimming\u003c\/h3\u003e\n\u003cp\u003eUltra-fast F\/2 systems like the RASA 8 have an extremely shallow depth of focus, in the tens of micrometers. Small mechanical tolerances in the telescope and camera bodies can move the best backfocus slightly, so fine adjustment with thin shim rings is recommended when tuning corner stars. Stars elongated on one side, or uneven focus across the corners, are typically caused by camera sensor tilt or telescope collimation, not the filter.\u003c\/p\u003e\n\u003cp\u003eTilt and collimation cannot be fixed by changing spacing. Use a camera tilt adjuster, or contact your telescope or camera manufacturer.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I install the IDAS OL7.5 filter on a Celestron RASA 8?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eInstallation is a simple 3-step process. First, attach the standard M42 camera adapter that came with your RASA 8. Second, thread the IDAS OL7.5 filter onto the adapter. Third, thread your camera with a 17.5mm flange-back distance onto the filter. This completes the required 25.0mm optical path.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eShould I get the M42 or M54 version of the IDAS OL7.5 for my RASA 8?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eChoose based on your sensor. For APS-C or Four Thirds sensors, the M42 version with its 37mm clear aperture is the match. For full-frame sensors or Duo cameras with a built-in guide sensor, IDAS recommends the M54 version with its 47mm clear aperture.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat does \"7.5mm optical path\" mean if the IDAS OL7.5 filter is 8.1mm thick?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003e8.1mm is the physical flange-to-flange length. The 2.0mm filter glass refracts light and pushes the focal plane back by about 0.6mm, so the net optical path consumption is exactly 7.5mm. Use 7.5mm in your backfocus calculation.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eMy stars are elongated in one corner with the IDAS OL7.5. Is the filter causing this?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eTypically not. On an F\/2 system like the RASA 8, stars elongated on one side or uneven corner focus are usually caused by camera sensor tilt or telescope collimation. These cannot be fixed by changing spacing; use a camera tilt adjuster or contact your telescope or camera manufacturer.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIf I buy the M54 IDAS OL7.5 for my RASA 8, do I need to buy the M42-M54 adapter separately?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo. Choose the \"M54 OL7.5 + M42-M54 adapter\" option and the adapter ring is included. It adds 0mm of optical path. Choose the M54 OL7.5 alone if your telescope already ends in an M54 male thread or you already own the adapter.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhy is the 47mm clear aperture of the M54 IDAS OL7.5 important for a ZWO Duo camera?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe 47mm clear aperture prevents frame clipping on the outer autoguiding sensor of Duo cameras such as the ZWO ASI2600MC Duo, and reduces vignetting on the main sensor.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eBrand\u003c\/td\u003e\n\u003ctd\u003eIDAS (ICAS Enterprises, Japan)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMount Options\u003c\/td\u003e\n\u003ctd\u003eM42 OL7.5 (37mm clear aperture); M54 OL7.5 (47mm clear aperture); M54 OL7.5 + 0mm path M42-M54 adapter\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eThreading\u003c\/td\u003e\n\u003ctd\u003eM42 P0.75 or M54 P0.75 (Male on camera side \/ Female on scope side)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOptical Path Length\u003c\/td\u003e\n\u003ctd\u003e7.5mm (accounts for 2.0mm glass refraction)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMechanical Length\u003c\/td\u003e\n\u003ctd\u003e8.1mm (flange to flange)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eGlass Thickness\u003c\/td\u003e\n\u003ctd\u003e2.0mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBackfocus Example\u003c\/td\u003e\n\u003ctd\u003eCelestron RASA 8 (25.0mm required) = 7.5mm filter + 17.5mm camera\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFilter Choices (M42)\u003c\/td\u003e\n\u003ctd\u003eClear, DTD, GNB, HEUIB-II, NB1, NGS1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFilter Choices (M54)\u003c\/td\u003e\n\u003ctd\u003eClear (ODW), GNB, HEUIB-II, NBZ-II, NGS1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCountry of Origin\u003c\/td\u003e\n\u003ctd\u003eMade in Japan\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eIDAS OL7.5 filter in the chosen mount and filter\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eIDAS M42-M54 adapter ring\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1 (M54 OL7.5 + adapter option only)\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul style=\"list-style: none; padding-left: 0;\"\u003e\u003cli style=\"margin-bottom: 1em;\"\u003e\u003ca href=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/idas-filter-cleaning-procedure.pdf\" target=\"_blank\"\u003eIDAS Filter Cleaning Procedure\u003c\/a\u003e\u003c\/li\u003e\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/idas-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eIDAS 3-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"IDAS","offers":[{"title":"Clear \/ M42 OL7.5","offer_id":68048466575645,"sku":"IDA-CLEAR-M42-OL7.5","price":108.0,"currency_code":"USD","in_stock":true},{"title":"Clear \/ M54 OL7.5","offer_id":68048466608413,"sku":"IDA-CLEAR-M54-OL7.5","price":111.0,"currency_code":"USD","in_stock":true},{"title":"Clear \/ M54 OL7.5 + M42-M54 adapter","offer_id":68048466641181,"sku":"IDA-CLEAR-M54-OL7.5-ADP","price":150.0,"currency_code":"USD","in_stock":true},{"title":"DTD \/ M42 OL7.5","offer_id":68048466673949,"sku":"IDA-DTD-M42-OL7.5","price":175.0,"currency_code":"USD","in_stock":true},{"title":"GNB \/ M42 OL7.5","offer_id":68048466706717,"sku":"IDA-GNB-M42-OL7.5","price":175.0,"currency_code":"USD","in_stock":true},{"title":"GNB \/ M54 OL7.5","offer_id":68048466739485,"sku":"IDA-GNB-M54-OL7.5","price":248.0,"currency_code":"USD","in_stock":true},{"title":"GNB \/ M54 OL7.5 + M42-M54 adapter","offer_id":68048466772253,"sku":"IDA-GNB-M54-OL7.5-ADP","price":268.0,"currency_code":"USD","in_stock":true},{"title":"HEUIB-II \/ M42 OL7.5","offer_id":68048466805021,"sku":"IDA-HEUIB-II-M42-OL7.5","price":175.0,"currency_code":"USD","in_stock":true},{"title":"HEUIB-II \/ M54 OL7.5","offer_id":68048466837789,"sku":"IDA-HEUIB-II-M54-OL7.5","price":198.0,"currency_code":"USD","in_stock":true},{"title":"HEUIB-II \/ M54 OL7.5 + M42-M54 adapter","offer_id":68048466870557,"sku":"IDA-HEUIB-II-M54-OL7.5-ADP","price":226.0,"currency_code":"USD","in_stock":true},{"title":"NB1 \/ M42 OL7.5","offer_id":68048466903325,"sku":"IDA-NB1-M42-OL7.5","price":175.0,"currency_code":"USD","in_stock":true},{"title":"NBZ-II \/ M54 OL7.5","offer_id":68048466936093,"sku":"IDA-NBZ-II-M54-OL7.5","price":318.0,"currency_code":"USD","in_stock":true},{"title":"NBZ-II \/ M54 OL7.5 + M42-M54 adapter","offer_id":68048466968861,"sku":"IDA-NBZ-II-M54-OL7.5-ADP","price":341.0,"currency_code":"USD","in_stock":true},{"title":"NGS1 \/ M42 OL7.5","offer_id":68048467001629,"sku":"IDA-NGS1-M42-OL7.5","price":175.0,"currency_code":"USD","in_stock":true},{"title":"NGS1 \/ M54 OL7.5","offer_id":68048467034397,"sku":"IDA-NGS1-M54-OL7.5","price":198.0,"currency_code":"USD","in_stock":true},{"title":"NGS1 \/ M54 OL7.5 + M42-M54 adapter","offer_id":68048467067165,"sku":"IDA-NGS1-M54-OL7.5-ADP","price":226.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/idas-ol7-5-low-profile-filter-for-celestron-rasa-8-1.jpg?v=1794421265","url":"https:\/\/davidastro.com\/en-us\/products\/idas-ol7-5-low-profile-filter-for-celestron-rasa-8","provider":"David Astro","version":"1.0","type":"link"}