{"product_id":"antlia-sii-2-5nm-ultra-narrowband-filter","title":"Antlia SII 2.5nm Ultra Narrowband Filter","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eIsolates Sulfur-II emission at 671.6nm and 673.1nm\u003c\/li\u003e\n\u003cli\u003eUltra-narrow 2.5nm FWHM bandpass\u003c\/li\u003e\n\u003cli\u003ePeak transmission of \u0026gt;=95%\u003c\/li\u003e\n\u003cli\u003eOut-of-band blocking at OD5 (0.001%)\u003c\/li\u003e\n\u003cli\u003eThermally stable quartz glass substrate\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\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\u003eAntlia SII 2.5nm Ultra Narrowband Filter\u003c\/h2\u003e\n\u003cp\u003eThe Antlia SII 2.5nm Ultra Narrowband Filter isolates the critical 671.6nm and 673.1nm sulfur-II emission lines with an exceptionally tight 2.5nm full width at half maximum (FWHM). It achieves a peak transmission of \u0026gt;=95% on its durable quartz glass substrate, while suppressing unwanted light to an optical density of OD5 (0.001%). Recommended for optics of f\/3.5 or slower, it has a 2mm thickness identical to existing standards, made with utmost care for parfocality.\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\u003eCore Optical Design: 2.5nm FWHM and \u0026gt;=95% Transmission\u003c\/h3\u003e\n\u003cp\u003eThe defining feature of the Antlia 2.5nm Ultra series is its extremely narrow bandpass. At just 2.5nm, this filter passes the SII lines while blocking most background light from the Moon and artificial sources. Antlia states that this narrower FWHM gives an exceptionally high signal-to-noise ratio for deep sky imaging, revealing fainter nebulosity against a darker sky background.\u003c\/p\u003e\n\u003cp\u003eThe narrow bandpass is paired with a specified peak transmission of \u0026gt;=95% at the SII wavelengths. Compared with its 3nm Pro series, Antlia states the quartz-based Ultra series has higher transmittance for the emission lines and estimates it improves signal by 20-30% in your images.\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\u003eSignal Integrity: OD5 Blocking and a Flat-Top Spectrum\u003c\/h3\u003e\n\u003cp\u003eOff-band rejection is as critical as in-band transmission. The Antlia SII 2.5nm Ultra filter provides blocking to an optical density of 5 (OD5), attenuating unwanted wavelengths by a factor of 100,000. Antlia designs this blocking to block interference from other wavelengths and minimize halos around bright stars.\u003c\/p\u003e\n\u003cp\u003eThe filter is engineered with a flat-top spectrum profile. This means it maintains its high transmission rate across its 2.5nm bandpass, rather than having a sharp peak that quickly falls off. Antlia states this minimizes the loss in transmission due to the central wavelength (CWL) shift.\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\u003eSubstrate \u0026amp; Build: 2mm Quartz Glass for Thermal Stability\u003c\/h3\u003e\n\u003cp\u003eAntlia builds the 2.5nm Ultra series on a quartz glass substrate, chosen for its ultra-low coefficient of thermal expansion and outstanding thermal and mechanical properties. Combined with Antlia's coating processes, this gives remarkable durability for imaging in the most challenging environmental conditions.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eParfocal Design:\u003c\/strong\u003e The 2mm thickness is identical to existing standards, and the filter is double-sided fine polished with utmost care for parfocality.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEdge Blackening:\u003c\/strong\u003e Unmounted filters have their edges blackened, and all filters are coated to the edge of the substrate to eliminate internal reflections from stray light.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIndividual Verification:\u003c\/strong\u003e Every filter is 100% scanned and comes with its actual measured spectrum, transmission and blocking (OD) data in the box.\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\u003eAntlia 2.5nm Ultra vs. 3nm Pro: A Signal-to-Noise Upgrade\u003c\/h3\u003e\n\u003cp\u003eCompared with the Antlia 3nm Pro series, the 2.5nm Ultra series is coated on quartz glass and has higher transmittance for the emission lines and a narrower FWHM of 2.5nm +0.3\/-0.1nm. Antlia estimates these filters improve signal by 20-30% in your images and says the narrower FWHM results in an exceptionally high signal-to-noise ratio for deep sky photography.\u003c\/p\u003e\n\u003cp\u003eBy rejecting more of the background sky glow, the 2.5nm filter helps pull out faint structural detail in emission nebulae.\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\"\u003eWhat is the main advantage of the Antlia SII 2.5nm Ultra filter over a 3nm filter?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe primary advantage is a higher signal-to-noise ratio. Compared with Antlia's 3nm Pro series, the Ultra has a tighter \u003cstrong\u003e2.5nm bandpass\u003c\/strong\u003e and, coated on quartz glass, higher transmittance at the SII lines (\u0026gt;=95%); Antlia estimates a 20-30% signal improvement. The tighter bandpass also rejects more background light, giving a darker sky background so fainter details in nebulae stand out more clearly.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill the Antlia SII 2.5nm filter work with my fast f\/4 telescope?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. f\/4 is within Antlia's recommendation of \u003cstrong\u003ef\/3.5 or slower\u003c\/strong\u003e for best optical performance. Very narrow filters see their central wavelength (CWL) shift in steep light cones, so at f-ratios faster than f\/3.5 you may see a reduction in transmission.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhy is quartz glass important for the Antlia SII 2.5nm Ultra filter?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003e\u003cstrong\u003eQuartz glass\u003c\/strong\u003e has an ultra-low thermal expansion coefficient with outstanding thermal and mechanical properties. Antlia states it also gives better fracture and scratch resistance and improved coating resilience to cleaning, for remarkable durability in challenging environmental conditions.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the Antlia SII 2.5nm filter perform on the Wizard Nebula (NGC 7380) from a suburb?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe Wizard Nebula is an emission nebula that emits Sulfur-II light along with H-alpha, so it is a suitable target. From a suburban location, the ultra-narrow \u003cstrong\u003e2.5nm FWHM\u003c\/strong\u003e blocks most broadband light pollution while passing the 671.6nm and 673.1nm lines, which helps separate the nebula from the bright sky background. SII is fainter than H-alpha, so plan for long total exposure time.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat does OD5 blocking mean for my images with the Antlia SII 2.5nm filter?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003e\u003cstrong\u003eOD5 blocking\u003c\/strong\u003e means the filter reduces out-of-band light to just 0.001% of its original intensity. Antlia designs it to block interference from other wavelengths and minimize halos around bright stars.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the Antlia SII 2.5nm filter parfocal with other Antlia filters?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eAntlia makes the SII 2.5nm filter to a thickness of \u003cstrong\u003e2mm\u003c\/strong\u003e, identical to existing standards, with utmost care for parfocality; the H-alpha and OIII 2.5nm Ultra filters share the same 2mm thickness. Antlia does not state parfocality with its other series, so check focus when mixing filters of different series or thickness.\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\u003eFilter Type\u003c\/td\u003e\n\u003ctd\u003eSII Ultra Narrowband (SHO 2.5nm Ultra Series)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCentral Wavelength (CWL)\u003c\/td\u003e\n\u003ctd\u003e671.6nm \/ 673.1nm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003ePeak Transmission\u003c\/td\u003e\n\u003ctd\u003e\u0026gt;=95% at 671.6nm \/ 673.1nm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFWHM (Bandwidth)\u003c\/td\u003e\n\u003ctd\u003e2.5nm (+0.3\/-0.1nm)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBlocking\u003c\/td\u003e\n\u003ctd\u003e\u0026gt;=OD5 (0.001%) out-of-band\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSpectrum Profile\u003c\/td\u003e\n\u003ctd\u003eFlat-Top\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eRecommended F-Ratio\u003c\/td\u003e\n\u003ctd\u003ef\/3.5 or slower\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSubstrate\u003c\/td\u003e\n\u003ctd\u003eQuartz Glass\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFilter Thickness\u003c\/td\u003e\n\u003ctd\u003e2mm (+\/-0.05mm on 2\" mounted, +\/-0.1mm on 36mm unmounted)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSurface Quality\u003c\/td\u003e\n\u003ctd\u003eDouble-sided fine polishing\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eEdge Treatment\u003c\/td\u003e\n\u003ctd\u003eCoated to the edge; unmounted filters are edge blackened\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMounting (2\" Version)\u003c\/td\u003e\n\u003ctd\u003eM48x0.75 threads, ultra-thin black anodized cell, laser engraved\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAvailable Sizes\u003c\/td\u003e\n\u003ctd\u003e36mm Round Unmounted, 2\" Mounted\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eQuality Control\u003c\/td\u003e\n\u003ctd\u003e100% of production scanned individually\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eNot Recommended For\u003c\/td\u003e\n\u003ctd\u003eSolar imaging, night visual observation\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\"\u003eMeasured spectrum, transmission and blocking (OD) data\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003eActual measured data for your filter\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n\u003cp\u003eThis product is covered by Antlia's 3-year warranty against delamination.\u003c\/p\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Antlia","offers":[{"title":"36mm Round Unmounted","offer_id":51932625043741,"sku":"ANT-SII-2.5NM-RD36","price":651.0,"currency_code":"CAD","in_stock":true},{"title":"2\" Mounted","offer_id":51932625076509,"sku":"ANT-SII-2.5NM-2","price":826.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/antlia-src-o3djCzwEw6Ac46Ac_88fe9e44-410c-4691-a48c-489be6e6b596.jpg?v=1792550001","url":"https:\/\/davidastro.com\/products\/antlia-sii-2-5nm-ultra-narrowband-filter","provider":"David Astro","version":"1.0","type":"link"}