{"title":"ZWO Narrowband Filters","description":"\u003cp\u003eExplore ZWO narrowband filters for emission-nebula astrophotography. Designed for use with monochrome cameras and compatible filter wheels, narrowband filters isolate key emission wavelengths to improve contrast and reveal structure in nebulae.\u003c\/p\u003e","products":[{"product_id":"zwo-2-inch-narrowband-filter-set-7nm","title":"ZWO 2\" H-alpha SII OIII 7nm Narrowband Filter Set.","description":"\u003ch2\u003eImproved ZWO Narrowband Filters\u003c\/h2\u003e\n\u003cp\u003eSince mid-2018, ZWO has supplied an improved version of their narrowband filters. The improvement is most noticeable when imaging night-sky landscapes containing very bright stars, particularly with the \u003cstrong\u003eH-alpha\u003c\/strong\u003e and \u003cstrong\u003eSII\u003c\/strong\u003e filters. With the updated \u003cstrong\u003eOIII\u003c\/strong\u003e filters, the difference is more subtle.\u003c\/p\u003e\n\u003cp\u003eProduction of the \u003cstrong\u003e2\" version\u003c\/strong\u003e began at the end of 2019 and it has only ever been available in this improved form. For this reason, ZWO did not apply a “Mark II” designation, as there was never an earlier version.\u003c\/p\u003e\n\u003ch2\u003eWhat Are Narrowband Filters Used For?\u003c\/h2\u003e\n\u003cp\u003eNarrowband filter sets are used to create high-contrast deep-sky images of emission and diffuse nebulae such as the Veil Nebula, Orion Nebula (M42), North America Nebula, Horsehead Nebula, as well as planetary nebulae including the Dumbbell (M27), Ring (M57), and Helix Nebula.\u003c\/p\u003e\n\u003cp\u003eThey can be used instead of, or in combination with, LRGB filters. Many astrophotographers also use narrowband filters under moonlight or from heavily light-polluted locations, as they significantly suppress light pollution while enhancing nebular detail.\u003c\/p\u003e\n\u003cp\u003eBy using longer exposure times, nebulosity brightness is increased while stars remain relatively subdued. The sky background stays darker, resulting in improved contrast.\u003c\/p\u003e\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilter size:\u003c\/strong\u003e 2\" mounted cell\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSurface quality:\u003c\/strong\u003e Fine-optically polished to 1\/4 wavefront accuracy\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFWHM:\u003c\/strong\u003e 7 ± 0.5 nm\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eGlass thickness:\u003c\/strong\u003e 2 mm\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cstrong\u003eThis filter set includes three filters:\u003c\/strong\u003e H-alpha, OIII, and SII.\u003c\/p\u003e\n\u003ch2\u003eFilter Characteristics\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eH-alpha (7nm)\u003c\/strong\u003e\u003cbr\u003eCentre wavelength: 656 nm. Transmission reaches approximately 90% (minimum 80%). This bandwidth is well suited for high-contrast imaging and revealing fine nebular detail, even in areas affected by strong light pollution.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eSII (7nm)\u003c\/strong\u003e\u003cbr\u003eCentre wavelength: 672 nm. Designed for imaging emission nebulae, planetary nebulae, and supernova remnants. Commonly combined with H-alpha and OIII filters for SHO (Hubble palette) astrophotography.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eOIII (7nm)\u003c\/strong\u003e\u003cbr\u003eCentre wavelength: 500 nm. Isolates OIII emission lines while blocking unwanted light, enabling dramatic nebular contrast and expanding imaging possibilities beyond traditional RGB methods.\u003c\/p\u003e\n\u003ch2\u003eFilter Installation Orientation\u003c\/h2\u003e\n\u003cp\u003eZWO recommends that, for their latest narrowband filters, the \u003cstrong\u003ecoated side should face the telescope\u003c\/strong\u003e.\u003c\/p\u003e\n\u003cp\u003eTo identify the coated side, place the filter on a clean surface and hold a small object (such as a pen) just above the glass:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eIf you see a \u003cstrong\u003esingle reflection\u003c\/strong\u003e, that is the coated side and it should face the telescope.\u003c\/li\u003e\n\u003cli\u003eIf you see a \u003cstrong\u003edouble reflection\u003c\/strong\u003e, that side has an anti-reflection coating and should face the camera sensor.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eImage below shows a double reflection — this side should face the camera:\u003c\/p\u003e\n\u003cp\u003e\u003cimg alt=\"Double reflection indicating camera-facing side\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-telescope.webp\"\u003e\u003c\/p\u003e\n\u003cp\u003eImage below shows a single reflection — this side should face the telescope:\u003c\/p\u003e\n\u003cp\u003e\u003cimg alt=\"Single reflection indicating telescope-facing side\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-camera-sensor.webp\"\u003e\u003c\/p\u003e\n\u003ch2\u003eTransmission Curve\u003c\/h2\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e \u003cimg alt=\"ZWO narrowband filter transmission curves\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cfigure class=\"attachment attachment--preview\"\u003e\u003cbr\u003e\u003c\/figure\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":42544499556529,"sku":"Z266-NB7nmD2","price":734.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/zwo-2-h-alpha-sii-oiii-7nm-narrowband-filter-set-839904.webp?v=1718480511"},{"product_id":"zwo-2-h-alpha-7nm-narrowband-filter","title":"ZWO 2\" H-alpha 7nm Narrowband Filter","description":"\u003cdiv class=\"product-description\"\u003e\n\u003ch2\u003eZWO 2\" H-alpha 7nm Narrowband Filter\u003c\/h2\u003e\n\u003cp\u003eThe \u003cstrong\u003eZWO 2\" H-alpha 7nm Narrowband Filter\u003c\/strong\u003e is designed to dramatically improve \u003cstrong\u003edeep-sky image contrast and detail\u003c\/strong\u003e by isolating the \u003cstrong\u003e656 nm hydrogen-alpha emission line\u003c\/strong\u003e—the dominant wavelength emitted by many nebulae.\u003c\/p\u003e\n\u003cp\u003eBy aggressively rejecting unwanted wavelengths, this filter suppresses \u003cstrong\u003elight pollution, moonlight, and sky glow\u003c\/strong\u003e, allowing faint nebulosity to stand out cleanly against a dark background. The result is higher signal-to-noise, sharper stars, and significantly improved contrast, even when imaging from light-polluted locations.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch3\u003eWhy H-alpha Is So Effective\u003c\/h3\u003e\n\u003cp\u003eHydrogen-alpha emission is the primary signal source in many of the most well-known deep-sky objects, including emission nebulae, diffuse nebulae, and planetary nebulae. A dedicated H-alpha filter allows these structures to be recorded with exceptional clarity while greatly reducing background noise.\u003c\/p\u003e\n\u003cp\u003eMany astrophotographers use an H-alpha filter when imaging under a bright Moon or from urban environments, as it effectively removes most artificial lighting while preserving nebular signal. Longer exposures further enhance nebulosity while stars remain smaller and better defined compared to broadband imaging.\u003c\/p\u003e\n\u003cp\u003eH-alpha data can be used on its own or combined with LRGB data to enhance nebular detail and contrast. For users not ready to commit to full H-S-O narrowband imaging, adding an H-alpha filter to an existing LRGB set is often the most effective first step.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch3\u003eUse with Colour Cameras\u003c\/h3\u003e\n\u003cp\u003eAlthough narrowband filters are traditionally associated with mono cameras, the ZWO H-alpha filter can also be used effectively with colour cameras. While it may seem counterintuitive, it provides a practical compromise when time or processing complexity must be kept to a minimum.\u003c\/p\u003e\n\u003cp\u003eThis approach works best with \u003cstrong\u003efast optical systems\u003c\/strong\u003e, typically \u003cstrong\u003ef\/8 and faster\u003c\/strong\u003e, where sufficient signal can be captured efficiently.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch3\u003eTechnical Specifications\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eFilter size: 2\"\u003c\/li\u003e\n\u003cli\u003eCentral wavelength: 656 nm (H-alpha)\u003c\/li\u003e\n\u003cli\u003eFWHM bandwidth: 7 ± 0.5 nm\u003c\/li\u003e\n\u003cli\u003ePeak transmission: approx. 90% (minimum 80%)\u003c\/li\u003e\n\u003cli\u003eFine-optically polished for accurate 1\/4 wavefront over both surfaces\u003c\/li\u003e\n\u003cli\u003eGlass thickness: 1.9 mm ± 0.03 mm\u003c\/li\u003e\n\u003cli\u003eTotal thickness: 7.5 mm (5 mm optical + 2.5 mm thread)\u003c\/li\u003e\n\u003cli\u003eOptical length: 5 mm\u003c\/li\u003e\n\u003cli\u003eThread: M48 × 0.75 (standard 2\" filter thread)\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eThe 7 nm bandpass is an excellent balance between contrast and signal strength, making it ideal for high-contrast H-alpha astrophotography and for revealing fine nebular detail even under challenging sky conditions.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch3\u003eFilter Orientation – Which Side Faces the Telescope?\u003c\/h3\u003e\n\u003cp\u003eZWO recommends that, for their latest Mark II narrowband filters, the \u003cstrong\u003ecoated side of the filter faces the telescope\u003c\/strong\u003e. While performance differences may be subtle, following this guidance ensures optimal results.\u003c\/p\u003e\n\u003cp\u003eTo identify the coated side, place the filter on a clean surface and hold a small object (such as a pen) close above it without touching the glass:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eIf you see a \u003cstrong\u003esingle reflection\u003c\/strong\u003e, that is the coated side — it should face the telescope.\u003c\/li\u003e\n\u003cli\u003eIf you see a \u003cstrong\u003edouble reflection\u003c\/strong\u003e, that side has an anti-reflection coating only and should face the camera.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eImage below shows a \u003cstrong\u003edouble reflection\u003c\/strong\u003e; this side should face the camera sensor:\u003c\/p\u003e\n\u003cimg alt=\"Double reflection indicating anti-reflection side facing the camera\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-telescope.webp\"\u003e\n\u003cp\u003eImage below shows a \u003cstrong\u003esingle reflection\u003c\/strong\u003e; this side should face the telescope:\u003c\/p\u003e\n\u003cimg alt=\"Single reflection indicating coated side facing the telescope\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-camera-sensor.webp\"\u003e\u003chr\u003e\n\u003ch3\u003eTransmission Curve\u003c\/h3\u003e\n\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e \u003cimg alt=\"Transmission curve for ZWO H-alpha, OIII and SII narrowband filters\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e \u003c\/a\u003e \u003cbr\u003e\u003cbr\u003e\n\u003cfigure\u003e\u003cimg alt=\"\" src=\"https:\/\/www.rothervalleyoptics.co.uk\/user\/products\/productimages\/airmini12.jpeg\"\u003e\u003c\/figure\u003e\n\u003cfigure\u003e\u003cimg alt=\"\" src=\"https:\/\/www.rothervalleyoptics.co.uk\/user\/products\/productimages\/airmini14.jpeg\"\u003e\u003c\/figure\u003e\n\u003c\/div\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":42544504045745,"sku":"Z267-Ha7nmD2","price":281.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/zwo-2-h-alpha-7nm-narrowband-filter-833188.webp?v=1718480511"},{"product_id":"zwo-2-oiii-7nm-narrowband-filter","title":"ZWO 2\" OIII 7nm Narrowband Filter","description":"\u003ch1\u003e\u003c\/h1\u003e\n\u003ch3\u003e\n\u003cstrong\u003eThe ZWO OIII 7nm narrowband filter\u003c\/strong\u003e\u003cspan\u003e \u003c\/span\u003eis designed for nebula observation allowing 7nm bandwidth of light centred on a wavelength of 500nm, which corresponds to OIII emission lines, blocking out all other light.  Adding the ZWO OIII narrowband filter to your imaging collection will help you go beyond the RGB imaging and will help capture your favourite nebulae in a totally new light.\u003c\/h3\u003e\n\u003cp\u003eNo matter how polluted your skies may be! Combine it with H-alpha and SII narrowband filters (SHO Set) for tricolour CCD astrophotography or use it with a H-alpha filter to create bicolour images.\u003c\/p\u003e\n\u003cp\u003eNarrowband filters are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae (i.e. M27 Dumbbell nebula, M57 Ring Nebula, Helix Nebula), just to mention few of well known nebulosity's. Narrowband filters are sometimes used instead of LRGB filter sets and sometimes in combination with them...However, if you don't yet want to commit to full narrowband H-S-O imaging, you might just buy them one-by-one and still be able to use them, i.e. a OIII filter could be used together with a H-alpha for bicolour astrophotography for certain deep sky objects, usually nebulosity's\u003c\/p\u003e\n\u003cp\u003eSome amateur astronomers would use narrowband filters when the Moon is out or if they live in heavily light polluted areas as these filters would practically eliminate the effects of light pollution as a side effect. By applying longer exposure time you will increase the brightness of the nebulosity whilst stars will still appear much fainter (thus smaller and sharper) than if they were imaged with LRGB filters. The sky's background will also stay darker hence contrast will be increased.\u003c\/p\u003e\n\u003cp\u003eWe would recommend to use narrowband filters with fast imaging telescopes with f\/8 and faster focal ratio.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTechnical Specifications of ZWO OIII Narrowband Filter\u003c\/strong\u003e\u003cbr\u003eSize: 2\" filter cell\u003cbr\u003eFine-optically polished to ensure accurate 1\/4 wavefront over both surfaces\u003cbr\u003eFWHM：7 ± 0.5nm\u003cbr\u003eThickness of glass: 1.9mm ± 0.03mm\u003cbr\u003eTotal Thickness: 7.5mm = 5mm + 2.5mm (thread)\u003cbr\u003eOptical Length: 5mm\u003cbr\u003eThread: M48*0.75 male thread (standard 2\" filter thread)\u003c\/p\u003e\n\u003cp\u003eThe ZWO OIII 7nm narrowband filter is designed for nebula observation allowing 7nm bandwidth of light centred on a wavelength of 500nm, which corresponds to OIII emission lines, blocking out all other light.  Adding the ZWO OIII narrowband filter to your imaging collection will help you go beyond the RGB imaging and will help capture your favourite nebulae in a totally new light, no matter how polluted your skies may be!\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWHICH DIRECTION TO INSTALL THE FILTERS IN?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is a tricky question as we asked various manufacturers and most of these manufacturers think that it doesn't matter, however the manufacturer of ZWO filters advises that in the case of their latest (mark II) narrowband filters the coated side of the filter should face the telescope. Well, there is nothing to loose to follow their advice, so lets do it. Now, how to find out which side is the coated? Open the case and remove the filter from its pouch and put it on top of the pouch as this is most likely the most dust free element in your surrounding. Now hold an item, i.e. a pen above the filter, close enough, but make sure that it won't touch the filter. If you see a single reflection as if it was a mirror, that's the coated side; that side should face the telescope. If you see a double reflection, that side has an anti-reflection coating only and it should face the camera sensor.\u003c\/p\u003e\n\u003cp\u003eImage below shows a double reflection of the pen, so that side should face the camera:\u003c\/p\u003e\n\u003cp\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-telescope.webp\"\u003e\u003c\/p\u003e\n\u003cp\u003eImage below shows a single reflection of the pen, so that side should face the telescope:\u003c\/p\u003e\n\u003cp\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-camera-sensor.webp\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTransmission Curve\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e\u003c\/a\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cdiv\u003e\n\u003cfigure data-trix-attachment='{\"contentType\":\"image\",\"height\":2243,\"url\":\"https:\/\/www.rothervalleyoptics.co.uk\/user\/products\/productimages\/airmini14.jpeg\",\"width\":1200}' data-trix-content-type=\"image\" class=\"attachment attachment--preview\"\u003e\n\u003cfigcaption class=\"attachment__caption\"\u003e\u003c\/figcaption\u003e\n\u003c\/figure\u003e\n\u003c\/div\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":42544504701105,"sku":"Z268-OIII7nmD2","price":281.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/zwo-2-oiii-7nm-narrowband-filter-502759.webp?v=1718480509"},{"product_id":"zwo-2-sii-7nm-narrowband-filter","title":"ZWO 2\" SII 7nm Narrowband Filter","description":"\u003ch1\u003eZWO 2\" SII 7nm Narrowband Filter\u003c\/h1\u003e\n\u003cp\u003e(Since mid 2018 ZWO supplies a new, improved version of their narrowband filters. The difference is visible when shooting night sky \"landscapes\" with very bright stars in the field of view, especially with the H-alpha and SII filters, the difference is very-very subtle when using the new OIII filters... Production of the 2\" version started in the end of 2019, so it has ever been only available in the improved version, therefore we did not add a Mark II sign to the title as there has never been a Mark I.)\u003c\/p\u003e\n\u003cp\u003eThe\u003cspan\u003e \u003c\/span\u003e\u003cstrong\u003eZWO SII 7nm narrowband filter\u003c\/strong\u003e\u003cspan\u003e \u003c\/span\u003epasses light at 672nm wavelength with a bandpass of 7nm which is designed for nebula observation and imaging. It is suitable for visual observation on most emission nebulae, planetary nebulae and supernova remnants, use it with H-alpha and OIII narrowband filters (SHO Set) for tricolor CCD astrophotography or use it with a H-alpha filter to create bicolor images of nebulosities.\u003c\/p\u003e\n\u003cp\u003eNarrowband filters are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae (i.e. M27 Dumbbell nebula, M57 Ring Nebula, Helix Nebula), just to mention few of well known nebulosities. Narroband filters are sometimes used instead of LRGB filter sets and sometimes in combination with them...However, if you don't yet want to commit to full narrowband H-S-O imaging, you might just buy them one-by-one and still be able to use them, i.e. a SII filter could be used together with a H-alpha for bicolor astrophotography for certain deep sky objects, usually nebulosities...\u003c\/p\u003e\n\u003cp\u003eSome amateur astronomers would use narrowband filters when the Moon is out or if they live in heavily light polluted areas as these filters would practically eliminate the effects of light pollution as a side effect. By applying longer exposure time you will increase the brightness of the nebulosity whilst stars will still apear much fainter (thus smaller and sharper) than if they were imaged with LRGB filters. The sky's background will also stay darker hence contrast will be increased.\u003c\/p\u003e\n\u003cp\u003eWe would recommend to use narrowband filters with fast imaging telescopes with f\/8 and faster focal ratio.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTechnical Specifications of ZWO Narrowband Filter Set\u003c\/strong\u003e\u003cbr\u003eSize: 2\" filter cell\u003cbr\u003eFine-optically polished to ensure accurate 1\/4 wavefront over both surfaces\u003cbr\u003eFWHM：7 ± 0.5nm\u003cbr\u003eThickness of glass: 1.9mm ± 0.03mm\u003cbr\u003eTotal Thickness: 7.5mm = 5mm + 2.5mm (thread)\u003cbr\u003eOptical Length: 5mm\u003cbr\u003eThread: M48*0.75 male thread (standard 2\" filter thread)\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWHICH DIRECTION TO INSTALL THE FILTERS IN?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is a tricky question as we asked various manufacturers and most of these manufacturers think that it doesn't matter, however the manufacturer of ZWO filters advises that in the case of their latest (mark II) narrowband filters the coated side of the filter should face the telescope. Well, there is nothing to loose to follow their advice, so lets do it. Now, how to find out which side is the coated? Open the case and remove the filter from its pouch and put it on top of the puch as this is most likely the most dustfree element in your surrounding. Now hold an item, i.e. a pen above the filter, close enough, but make sure that it won't touch the filter. If you see a single reflection as if it was a mirror, that's the coated side; that side should face the telescope. If you see a double reflection, that side has an anti-reflection coating only and it should face the camera sensor.\u003c\/p\u003e\n\u003cp\u003eImage below shows a double reflection of the pen, so that side should face the camera:\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-telescope.webp\" alt=\"\"\u003e\u003c\/p\u003e\n\u003cp\u003eImage below shows a single reflection of the pen, so that side should face the telescope:\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-camera-sensor.webp\" alt=\"\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTransmission Curve\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/strong\u003e\u003c\/p\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":42544505487537,"sku":"Z269-SII7nmD2","price":281.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/zwo-2-sii-7nm-narrowband-filter-826201.webp?v=1718480522"},{"product_id":"zwo-31mm-h-alpha-7nm-narrowband-filter-unmounted-mark-ii-1","title":"ZWO 31mm H-alpha 7nm Narrowband Filter - UNMOUNTED - Mark II","description":"\u003ch3\u003eNarrowband filters are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae (i.e. M27 Dumbbell nebula, M57 Ring Nebula, Helix Nebula), just to mention few of well known nebulosities. Narroband filter sets are sometimes used instead of LRGB filter sets and sometimes in combination with them... However, if you don't yet want to commit to full narrowband H-S-O imaging, it could be a good start to add just a H-alpha filter to your collection of LRGB filters or you might even use it just on its own as we'll explain below...\u003cbr\u003e\n\u003c\/h3\u003e\n\u003cp\u003eSome amateur astronomers would use a H-alpha filter when the Moon is out or if they live in heavily light polluted areas as these filters would practically eliminate the effects of light pollution as a side effect. By applying longer exposure time you will increase the brightness of the nebulosity whilst stars will still appear much fainter (thus smaller and sharper) than if they were imaged with LRGB filters. The sky's background will also stay darker hence contrast will be increased. Many amateurs would use a H-alpha filter in combination with an LRGB set for certain objects, mainly nebulosity's.\u003c\/p\u003e\n\u003cp\u003eOthers would use a H-alpha filter with a colour camera. Although it might seem counter productive, but it is a good compromise when you don't want to spend lots of time with post processing, but sometimes you need that extra narrowband data for a deep sky object... best to use it with fast imaging telescopes with f\/8 and faster focal ratio.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTechnical Specifications of ZWO H-alpha Narrowband Filter\u003c\/strong\u003e\u003cbr\u003eSize: 31mm unmounted\u003cbr\u003eFine-optically polished to ensure accurate 1\/4 wavefront over both surfaces\u003cbr\u003eFWHM：7 ± 0.5nm\u003cbr\u003eThickness of glass: 1.9mm ± 0.03mm\u003cbr\u003eTotal Thickness: 9mm = 5.5mm + 3.5mm (thread)\u003cbr\u003eOptical Length: 5.5mm\u003cbr\u003eThread: M28.5*0.6 male thread (standard 1.25\" filter thread)\u003cbr\u003e\u003cbr\u003eThe ZWO H-Alpha filter has a bandpass of 7nm and passes light at 656nm wavelength. The light transmission rate comes up to appr. 90% (min. 80%). A 7nm type is a very good choice for narrowband H-alpha astrophotography for high-contrast imaging and revealing rich details of a nebula even in areas with strong light pollution, so prepare to have lots of fun with it!\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWHICH DIRECTION TO INSTALL THE FILTERS IN?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is a tricky question as we asked various manufacturers and most of these manufacturers think that it doesn't matter, however the manufacturer of ZWO filters advises that in the case of their latest (mark II) narrowband filters the coated side of the filter should face the telescope. Well, there is nothing to loose to follow their advice, so lets do it. Now, how to find out which side is the coated? Open the case and remove the filter from its pouch and put it on top of the pouch as this is most likely the most dust free element in your surrounding. Now hold an item, i.e. a pen above the filter, close enough, but make sure that it won't touch the filter. If you see a single reflection as if it was a mirror, that's the coated side; that side should face the telescope. If you see a double reflection, that side has an anti-reflection coating only and it should face the camera sensor.\u003c\/p\u003e\n\u003cp\u003eImage below shows a double reflection of the pen, so that side should face the camera:\u003c\/p\u003e\n\u003cp\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-telescope.webp\"\u003e\u003c\/p\u003e\n\u003cp\u003eImage below shows a single reflection of the pen, so that side should face the telescope:\u003c\/p\u003e\n\u003cp\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-camera-sensor.webp\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTransmission Curve\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e\u003c\/a\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eComparison of New (Mark II) and Old Narrowband filters:\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) Ha filter is based on a new base glass, resulting in less reflection (i.e. less halo around bright stars).\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-H-alpha-narrowband-filter-compare1.webp\"\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-H-alpha-narrowband-filter-compare1.webp\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) SII filter is based on a new base glass, resulting in less reflection (i.e. less halo around bright stars).\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-SII-narrowband-filter-compare1.webp\"\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-SII-narrowband-filter-compare1.webp\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) OIII filter is based on the same base glass, but with a new standard coating, resulting in improved blocking of off-band light.\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-OIII-narrowband-filter-compare1.webp\"\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-OIII-narrowband-filter-compare1.webp\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eHere is a sample image of a test comparison of the old and new ZWO narrowband Ha Filters (ASI1600 mono camera, single frame, 300s, DDP in MaximDL). \u003c\/p\u003e\n\u003cp\u003eThe difference is subtle, but visible, especially when there are really bright stars in the field of view:\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/ZWO-Narrowband-h-alpha-real-test-new-2018-mark-II-filters-02.webp\"\u003e\u003cimg alt=\"\" src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/ZWO-Narrowband-h-alpha-real-test-new-2018-mark-II-filters-02.webp\"\u003e\u003c\/a\u003e\u003c\/p\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":42544506306737,"sku":"Z258-Ha7nmD31MkII","price":154.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/zwo-31mm-h-alpha-7nm-narrowband-filter-unmounted-mark-ii-611701.webp?v=1718480515"},{"product_id":"zwo-31mm-h-alpha-sii-oiii-7nm-narrowband-filter-set-unmounted-mark-ii","title":"ZWO 31mm H-alpha, SII, OIII 7nm Narrowband Filter Set - UNMOUNTED - Mark II","description":"\u003ch3\u003eNarrowband filters are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae (i.e. M27 Dumbbell nebula, M57 Ring Nebula, Helix Nebula), just to mention few of well known nebulosities. Narroband filter sets are sometimes used instead of LRGB filter sets and sometimes in combination with them... However, if you don't yet want to commit to full narrowband H-S-O imaging, it could be a good start to add just a H-alpha filter to your collection of LRGB filters or you might even use it just on its own as we'll explain below...\u003cbr\u003e\n\u003c\/h3\u003e\n\u003cp\u003eSome amateur astronomers would use a H-alpha filter when the Moon is out or if they live in heavily light polluted areas as these filters would practically eliminate the effects of light pollution as a side effect. By applying longer exposure time you will increase the brightness of the nebulosity whilst stars will still appear much fainter (thus smaller and sharper) than if they were imaged with LRGB filters. The sky's background will also stay darker hence contrast will be increased. Many amateurs would use a H-alpha filter in combination with an LRGB set for certain objects, mainly nebulosity's.\u003c\/p\u003e\n\u003cp\u003eOthers would use a H-alpha filter with a colour camera. Although it might seem counter productive, but it is a good compromise when you don't want to spend lots of time with post processing, but sometimes you need that extra narrowband data for a deep sky object... best to use it with fast imaging telescopes with f\/8 and faster focal ratio.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTechnical Specifications of ZWO H-alpha Narrowband Filter\u003c\/strong\u003e\u003cbr\u003eSize: 31mm unmounted\u003cbr\u003eFine-optically polished to ensure accurate 1\/4 wavefront over both surfaces\u003cbr\u003eFWHM：7 ± 0.5nm\u003cbr\u003eThickness of glass: 1.9mm ± 0.03mm\u003cbr\u003eTotal Thickness: 9mm = 5.5mm + 3.5mm (thread)\u003cbr\u003eOptical Length: 5.5mm\u003cbr\u003eThread: M28.5*0.6 male thread (standard 1.25\" filter thread)\u003cbr\u003e\u003cbr\u003eThe ZWO H-Alpha filter has a bandpass of 7nm and passes light at 656nm wavelength. The light transmission rate comes up to appr. 90% (min. 80%). A 7nm type is a very good choice for narrowband H-alpha astrophotography for high-contrast imaging and revealing rich details of a nebula even in areas with strong light pollution, so prepare to have lots of fun with it!\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWHICH DIRECTION TO INSTALL THE FILTERS IN?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is a tricky question as we asked various manufacturers and most of these manufacturers think that it doesn't matter, however the manufacturer of ZWO filters advises that in the case of their latest (mark II) narrowband filters the coated side of the filter should face the telescope. Well, there is nothing to loose to follow their advice, so lets do it. Now, how to find out which side is the coated? Open the case and remove the filter from its pouch and put it on top of the pouch as this is most likely the most dust free element in your surrounding. Now hold an item, i.e. a pen above the filter, close enough, but make sure that it won't touch the filter. If you see a single reflection as if it was a mirror, that's the coated side; that side should face the telescope. If you see a double reflection, that side has an anti-reflection coating only and it should face the camera sensor.\u003c\/p\u003e\n\u003cp\u003eImage below shows a double reflection of the pen, so that side should face the camera:\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/ZWO-Narrowband-h-alpha-real-test-new-2018-mark-II-filters-02.webp\"\u003e\u003c\/p\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":42544506732721,"sku":"Z255-NB7nmD31MkII","price":452.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/zwo-31mm-h-alpha-sii-oiii-7nm-narrowband-filter-set-unmounted-mark-ii-176650.webp?v=1718480522"},{"product_id":"zwo-31mm-oiii-7nm-narrowband-filter-unmounted-mark-ii","title":"ZWO 31mm OIII 7nm Narrowband Filter - UNMOUNTED - Mark II","description":"\u003ch1\u003e\n\u003cstrong\u003eThe ZWO OIII 7nm narrowband filter\u003c\/strong\u003e\u003cspan\u003e \u003c\/span\u003eis designed for nebula observation allowing 7nm bandwidth of light centered on a wavelength of 500nm, which corresponds to OIII emission lines, blocking out all other light.  \u003cbr\u003e\n\u003c\/h1\u003e\n\u003cp\u003eAdding the ZWO OIII narrowband filter to your imaging collection will help you go beyond the RGB imaging and will help capture your favorite nebulae in a totally new light, no matter how polluted your skies may be! Combine it with H-alpha and SII narrowband filters (SHO Set) for tricolor CCD astrophotography or use it with a H-alpha filter to create bicolor images.\u003c\/p\u003e\n\u003cp\u003e(Since mid 2018 ZWO supplies a new, improved version of their narrowband filters. The difference is visible when shooting night sky \"landscapes\" with very bright stars in the field of view, especially with the H-alpha and SII filters, the difference is very-very subtle when using the new OIII filters...)\u003c\/p\u003e\n\u003cp\u003eNarrowband filters are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae (i.e. M27 Dumbbell nebula, M57 Ring Nebula, Helix Nebula), just to mention few of well known nebulosities. Narroband filters are sometimes used instead of LRGB filter sets and sometimes in combination with them...However, if you don't yet want to commit to full narrowband H-S-O imaging, you might just buy them one-by-one and still be able to use them, i.e. a OIII filter could be used together with a H-alpha for bicolor astrophotography for certain deep sky objects, usually nebulosities...\u003c\/p\u003e\n\u003cp\u003eSome amateur astronomers would use narrowband filters when the Moon is out or if they live in heavily light polluted areas as these filters would practically eliminate the effects of light pollution as a side effect. By applying longer exposure time you will increase the brightness of the nebulosity whilst stars will still apear much fainter (thus smaller and sharper) than if they were imaged with LRGB filters. The sky's background will also stay darker hence contrast will be increased.\u003c\/p\u003e\n\u003cp\u003eWe would recommend to use narrowband filters with fast imaging telescopes with f\/8 and faster focal ratio.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTechnical Specifications of ZWO OIII Narrowband Filter\u003c\/strong\u003e\u003cbr\u003eSize: 31mm\u003cbr\u003eFine-optically polished to ensure accurate 1\/4 wavefront over both surfaces\u003cbr\u003eFWHM：7 ± 0.5nm\u003cbr\u003eThickness of glass: 1.9mm ± 0.03mm\u003cbr\u003eTotal Thickness: 9mm = 5.5mm + 3.5mm (thread)\u003cbr\u003eOptical Length: 5.5mm\u003cbr\u003eThread: M28.5*0.6 male thread (standard 1.25\" filter thread)\u003c\/p\u003e\n\u003cp\u003eThe ZWO OIII 7nm narrowband filter is designed for nebula observation allowing 7nm bandwidth of light centered on a wavelength of 500nm, which corresponds to OIII emission lines, blocking out all other light.  Adding the ZWO OIII narrowband filter to your imaging collection will help you go beyond the RGB imaging and will help capture your favorite nebulae in a totally new light, no matter how polluted your skies may be!\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWHICH DIRECTION TO INSTALL THE FILTERS IN?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is a tricky question as we asked various manufacturers and most of these manufacturers think that it doesn't matter, however the manufacturer of ZWO filters advises that in the case of their latest (mark II) narrowband filters the coated side of the filter should face the telescope. Well, there is nothing to loose to follow their advice, so lets do it. Now, how to find out which side is the coated? Open the case and remove the filter from its pouch and put it on top of the puch as this is most likely the most dustfree element in your surrounding. Now hold an item, i.e. a pen above the filter, close enough, but make sure that it won't touch the filter. If you see a single reflection as if it was a mirror, that's the coated side; that side should face the telescope. If you see a double reflection, that side has an anti-reflection coating only and it should face the camera sensor.\u003c\/p\u003e\n\u003cp\u003eImage below shows a double reflection of the pen, so that side should face the camera:\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-telescope.webp\" alt=\"\"\u003e\u003c\/p\u003e\n\u003cp\u003eImage below shows a single reflection of the pen, so that side should face the telescope:\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-camera-sensor.webp\" alt=\"\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTransmission Curve\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eComparison of New (Mark II) and Old Narrowband filters:\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) Ha filter is based on a new base glass, resulting in less reflection (i.e. less halo around bright stars).\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-H-alpha-narrowband-filter-compare1.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-H-alpha-narrowband-filter-compare1.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) SII filter is based on a new base glass, resulting in less reflection (i.e. less halo around bright stars).\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-SII-narrowband-filter-compare1.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-SII-narrowband-filter-compare1.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) OIII filter is based on the same base glass, but with a new standard coating, resulting in improved blocking of off-band light.\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-OIII-narrowband-filter-compare1.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-OIII-narrowband-filter-compare1.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eHere is a sample image of a test comparison of the old and new ZWO narrowband Ha Filters (ASI1600 mono camera, single frame, 300s, DDP in MaximDL). \u003c\/p\u003e\n\u003cp\u003eThe difference is subtle, but visible, especially when there are really bright stars in the field of view:\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/ZWO-Narrowband-h-alpha-real-test-new-2018-mark-II-filters-02.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/ZWO-Narrowband-h-alpha-real-test-new-2018-mark-II-filters-02.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/p\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":42544506798257,"sku":"Z261-OIII7nmD31MkII","price":154.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/zwo-31mm-oiii-7nm-narrowband-filter-unmounted-mark-ii-495640.webp?v=1718480589"},{"product_id":"zwo-31mm-sii-7nm-narrowband-filter-unmounted-mark-ii","title":"ZWO 31mm SII 7nm Narrowband Filter - UNMOUNTED - Mark II","description":"\u003ch1\u003eZWO 31mm SII 7nm Narrowband Filter - UNMOUNTED - Mark II\u003c\/h1\u003e\n\u003cp\u003e(Since mid 2018 ZWO supplies a new, improved version of their narrowband filters. The difference is visible when shooting night sky \"landscapes\" with very bright stars in the field of view, especially with the H-alpha and SII filters, the difference is very-very subtle when using the new OIII filters...)\u003c\/p\u003e\n\u003cp\u003eThe\u003cspan\u003e \u003c\/span\u003e\u003cstrong\u003eZWO SII 7nm narrowband filter\u003c\/strong\u003e\u003cspan\u003e \u003c\/span\u003epasses light at 672nm wavelength with a bandpass of 7nm which is designed for nebula observation and imaging. It is suitable for visual observation on most emission nebulae, planetary nebulae and supernova remnants, use it with H-alpha and OIII narrowband filters (SHO Set) for tricolor CCD astrophotography or use it with a H-alpha filter to create bicolor images of nebulosities.\u003c\/p\u003e\n\u003cp\u003eNarrowband filters are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae (i.e. M27 Dumbbell nebula, M57 Ring Nebula, Helix Nebula), just to mention few of well known nebulosities. Narroband filters are sometimes used instead of LRGB filter sets and sometimes in combination with them...However, if you don't yet want to commit to full narrowband H-S-O imaging, you might just buy them one-by-one and still be able to use them, i.e. a SII filter could be used together with a H-alpha for bicolor astrophotography for certain deep sky objects, usually nebulosities...\u003c\/p\u003e\n\u003cp\u003eSome amateur astronomers would use narrowband filters when the Moon is out or if they live in heavily light polluted areas as these filters would practically eliminate the effects of light pollution as a side effect. By applying longer exposure time you will increase the brightness of the nebulosity whilst stars will still apear much fainter (thus smaller and sharper) than if they were imaged with LRGB filters. The sky's background will also stay darker hence contrast will be increased.\u003c\/p\u003e\n\u003cp\u003eWe would recommend to use narrowband filters with fast imaging telescopes with f\/8 and faster focal ratio.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTechnical Specifications of ZWO Narrowband Filter Set\u003c\/strong\u003e\u003cbr\u003eSize: 31mm\u003cbr\u003eFine-optically polished to ensure accurate 1\/4 wavefront over both surfaces\u003cbr\u003eFWHM：7 ± 0.5nm\u003cbr\u003eThickness of glass: 1.9mm ± 0.03mm\u003cbr\u003eTotal Thickness: 9mm = 5.5mm + 3.5mm (thread)\u003cbr\u003eOptical Length: 5.5mm\u003cbr\u003eThread: M28.5*0.6 male thread (standard 1.25\" filter thread)\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWHICH DIRECTION TO INSTALL THE FILTERS IN?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is a tricky question as we asked various manufacturers and most of these manufacturers think that it doesn't matter, however the manufacturer of ZWO filters advises that in the case of their latest (mark II) narrowband filters the coated side of the filter should face the telescope. Well, there is nothing to loose to follow their advice, so lets do it. Now, how to find out which side is the coated? Open the case and remove the filter from its pouch and put it on top of the puch as this is most likely the most dustfree element in your surrounding. Now hold an item, i.e. a pen above the filter, close enough, but make sure that it won't touch the filter. If you see a single reflection as if it was a mirror, that's the coated side; that side should face the telescope. If you see a double reflection, that side has an anti-reflection coating only and it should face the camera sensor.\u003c\/p\u003e\n\u003cp\u003eImage below shows a double reflection of the pen, so that side should face the camera:\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-telescope.webp\" alt=\"\"\u003e\u003c\/p\u003e\n\u003cp\u003eImage below shows a single reflection of the pen, so that side should face the telescope:\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/narrowband-filter-facing-towards-camera-sensor.webp\" alt=\"\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTransmission Curve\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/lj\/product\/ZWO-Narrowband-h-alpha-oiii-sii-filters-transmission-curve-02.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eComparison of New (Mark II) and Old Narrowband filters:\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) Ha filter is based on a new base glass, resulting in less reflection (i.e. less halo around bright stars).\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-H-alpha-narrowband-filter-compare1.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-H-alpha-narrowband-filter-compare1.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) SII filter is based on a new base glass, resulting in less reflection (i.e. less halo around bright stars).\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-SII-narrowband-filter-compare1.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-SII-narrowband-filter-compare1.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eThe New (Mark II) OIII filter is based on the same base glass, but with a new standard coating, resulting in improved blocking of off-band light.\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-OIII-narrowband-filter-compare1.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/new-zwo-2018-OIII-narrowband-filter-compare1.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/p\u003e\n\u003cp\u003eHere is a sample image of a test comparison of the old and new ZWO narrowband Ha Filters (ASI1600 mono camera, single frame, 300s, DDP in MaximDL). \u003c\/p\u003e\n\u003cp\u003eThe difference is subtle, but visible, especially when there are really bright stars in the field of view:\u003c\/p\u003e\n\u003cp\u003e\u003ca href=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/ZWO-Narrowband-h-alpha-real-test-new-2018-mark-II-filters-02.webp\"\u003e\u003cimg src=\"https:\/\/www.365astronomy.com\/image\/cache\/wp\/ij\/content\/ZWO-Narrowband-h-alpha-real-test-new-2018-mark-II-filters-02.webp\" alt=\"\"\u003e\u003c\/a\u003e\u003c\/p\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":42544507453617,"sku":"Z264-SII7nmD31MkII","price":154.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/zwo-31mm-sii-7nm-narrowband-filter-unmounted-mark-ii-756263.webp?v=1718480590"},{"product_id":"zwo-duo-band-filter-1-25","title":"ZWO Duo-Band Dual-Bandpass Narrowband Imaging Filter - 1.25\"","description":"\u003cp\u003eThe ZWO Duo-Band Filter is a dual narrowband imaging filter designed for one-shot colour (OSC) astronomy cameras. By isolating the important H-alpha (656.3nm) and OIII (500nm) emission lines, it enhances contrast in nebulae while reducing the effects of moonlight and urban light pollution.\u003c\/p\u003e\n\n\u003cp\u003eIdeal for deep-sky astrophotography, the Duo-Band filter allows colour camera users to capture narrowband-style images without the need for a monochrome camera, filter wheel and multiple filters.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eKey Features\u003c\/strong\u003e\u003c\/p\u003e\n\n\u003cul\u003e\n\u003cli\u003eDual-bandpass design for H-alpha and OIII emission lines\u003c\/li\u003e\n\u003cli\u003eImproves contrast on emission nebulae\u003c\/li\u003e\n\u003cli\u003eReduces light pollution and moonlight interference\u003c\/li\u003e\n\u003cli\u003eExcellent choice for one-shot colour cameras\u003c\/li\u003e\n\u003cli\u003eCompatible with ZWO ASI cameras and EFW filter wheels\u003c\/li\u003e\n\u003cli\u003ePrecision optical coatings for high transmission and minimal reflections\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-1-1000x1000w.webp?v=1782214793\" alt=\"ZWO Duo-Band Filter\"\u003e\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eTechnical Specifications\u003c\/strong\u003e\u003c\/p\u003e\n\n\u003cul\u003e\n\u003cli\u003eAvailable Sizes: 1.25\" and 2\"\u003c\/li\u003e\n\u003cli\u003eFilter Thickness: 1.85mm\u003c\/li\u003e\n\u003cli\u003eH-alpha Bandwidth: 15nm\u003c\/li\u003e\n\u003cli\u003eOIII Bandwidth: 35nm\u003c\/li\u003e\n\u003cli\u003eSchott optical glass substrate\u003c\/li\u003e\n\u003cli\u003e\u0026gt;90% transmission at OIII wavelengths\u003c\/li\u003e\n\u003cli\u003e\u0026gt;80% transmission at H-alpha wavelength\u003c\/li\u003e\n\u003cli\u003eSurface Quality: 60\/40 (MIL-O-13830)\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-1.25-inch-1000x1000w.webp?v=1782214794\" alt=\"ZWO Duo-Band Filter 1.25\"\u003e\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003ePrecision Construction\u003c\/strong\u003e\u003c\/p\u003e\n\n\u003cul\u003e\n\u003cli\u003eCNC-machined aerometal housing\u003c\/li\u003e\n\u003cli\u003eFine sandblasted and anodised finish\u003c\/li\u003e\n\u003cli\u003eAnti-reflection extinction treatment\u003c\/li\u003e\n\u003cli\u003eLaser engraved markings\u003c\/li\u003e\n\u003cli\u003eDouble-sided precision optical coatings\u003c\/li\u003e\n\u003cli\u003eOptically polished for excellent wavefront accuracy\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-2.webp?v=1782214794\" alt=\"Filter Transmission Diagram\"\u003e\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eImportant Note\u003c\/strong\u003e\u003c\/p\u003e\n\n\u003cp\u003eFor optimum performance, incoming light should strike the filter as close to perpendicular as possible. This filter is not recommended for use with wide-angle or ultra-wide-angle camera lenses.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eReal-World Results\u003c\/strong\u003e\u003c\/p\u003e\n\n\u003cp\u003eThe examples below demonstrate the improvement in nebula contrast and detail when using the ZWO Duo-Band Filter in light-polluted conditions.\u003c\/p\u003e\n\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-10.webp?v=1782214795\" alt=\"Duo-Band Filter Example\"\u003e\u003c\/p\u003e\n\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-30.webp?v=1782214795\" alt=\"Duo-Band Filter Imaging Example\"\u003e\u003c\/p\u003e\n\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-20.webp?v=1782214794\" alt=\"Duo-Band Filter Comparison\"\u003e\u003c\/p\u003e\n","brand":"ZWO","offers":[{"title":"Default Title","offer_id":55587436134776,"sku":"Z212-DB1.25","price":99.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-1.25-inch-1000x1000w.webp?v=1782294405"},{"product_id":"zwo-duo-band-dual-bandpass-narrowband-imaging-filter-2","title":"ZWO Duo-Band Dual-Bandpass Narrowband Imaging Filter - 2\"","description":"\u003cp\u003eThe ZWO Duo-Band Filter is a dual narrowband imaging filter designed for one-shot colour (OSC) astronomy cameras. By isolating the important H-alpha (656.3nm) and OIII (500nm) emission lines, it enhances contrast in nebulae while reducing the effects of moonlight and urban light pollution.\u003c\/p\u003e\n\u003cp\u003eIdeal for deep-sky astrophotography, the Duo-Band filter allows colour camera users to capture narrowband-style images without the need for a monochrome camera, filter wheel and multiple filters.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eKey Features\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eDual-bandpass design for H-alpha and OIII emission lines\u003c\/li\u003e\n\u003cli\u003eImproves contrast on emission nebulae\u003c\/li\u003e\n\u003cli\u003eReduces light pollution and moonlight interference\u003c\/li\u003e\n\u003cli\u003eExcellent choice for one-shot colour cameras\u003c\/li\u003e\n\u003cli\u003eCompatible with ZWO ASI cameras and EFW filter wheels\u003c\/li\u003e\n\u003cli\u003ePrecision optical coatings for high transmission and minimal reflections\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-1-1000x1000w.webp?v=1782214793\" alt=\"ZWO Duo-Band Filter\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTechnical Specifications\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eAvailable Sizes: 1.25\" and 2\"\u003c\/li\u003e\n\u003cli\u003eFilter Thickness: 1.85mm\u003c\/li\u003e\n\u003cli\u003eH-alpha Bandwidth: 15nm\u003c\/li\u003e\n\u003cli\u003eOIII Bandwidth: 35nm\u003c\/li\u003e\n\u003cli\u003eSchott optical glass substrate\u003c\/li\u003e\n\u003cli\u003e\u0026gt;90% transmission at OIII wavelengths\u003c\/li\u003e\n\u003cli\u003e\u0026gt;80% transmission at H-alpha wavelength\u003c\/li\u003e\n\u003cli\u003eSurface Quality: 60\/40 (MIL-O-13830)\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-2-inch-1000x1000w.webp?v=1782215386\" alt=\"\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003ePrecision Construction\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eCNC-machined aerometal housing\u003c\/li\u003e\n\u003cli\u003eFine sandblasted and anodised finish\u003c\/li\u003e\n\u003cli\u003eAnti-reflection extinction treatment\u003c\/li\u003e\n\u003cli\u003eLaser engraved markings\u003c\/li\u003e\n\u003cli\u003eDouble-sided precision optical coatings\u003c\/li\u003e\n\u003cli\u003eOptically polished for excellent wavefront accuracy\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-2.webp?v=1782214794\" alt=\"Filter Transmission Diagram\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eImportant Note\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eFor optimum performance, incoming light should strike the filter as close to perpendicular as possible. This filter is not recommended for use with wide-angle or ultra-wide-angle camera lenses.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eReal-World Results\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe examples below demonstrate the improvement in nebula contrast and detail when using the ZWO Duo-Band Filter in light-polluted conditions.\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-10.webp?v=1782214795\" alt=\"Duo-Band Filter Example\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-30.webp?v=1782214795\" alt=\"Duo-Band Filter Imaging Example\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-20.webp?v=1782214794\" alt=\"Duo-Band Filter Comparison\"\u003e\u003c\/p\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":55587440427384,"sku":"Z212-DB2","price":168.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0523\/1650\/4241\/files\/ZWO-Duo-Band-Filter-dual-narrowband-filter-2-inch-1000x1000w.webp?v=1782294412"}],"url":"https:\/\/www.darkclearskies.co.uk\/collections\/zwo-narrowband-filters.oembed","provider":"Dark Clear Skies ","version":"1.0","type":"link"}