{"product_id":"optolong-oiii-18nm-filter","title":"Optolong OIII 18nm Nebula Filter","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003e18nm Bandpass Centered on OIII Emission Lines (500nm)\u003c\/li\u003e\n\u003cli\u003eGreater than 80% Average Light Transmission (Tave)\u003c\/li\u003e\n\u003cli\u003eBlocks \u0026gt;99% of Major Light Pollution Lines\u003c\/li\u003e\n\u003cli\u003e1.85mm Thick Optical Glass Substrate\u003c\/li\u003e\n\u003cli\u003eλ\/4 Transmitted Wavefront and 60\/40 Surface Quality\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\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\u003eOptolong OIII 18nm Nebula Filter\u003c\/h2\u003e\n\u003cp\u003eThe Optolong OIII 18nm Nebula Filter isolates the critical 500nm emission lines from planetary nebulae and supernova remnants with its focused 18nm bandpass. By achieving over 80% average transmission at these key wavelengths while blocking more than 99% of light pollution within its 400-700nm range, this filter dramatically increases contrast. The optically flat λ\/4 wavefront ensures your telescope's resolution is preserved, delivering sharp, high-contrast views even from suburban skies.\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\u003eIsolating Nebulae: The 18nm OIII Passband\u003c\/h3\u003e\n\u003cp\u003eThis filter is engineered to transmit a specific 18nm sliver of the blue-green spectrum, centered at 500nm. This window precisely captures the light from doubly ionized oxygen (OIII), the primary emission from targets like the Dumbbell Nebula (M27) and the Veil Nebula (NGC 6960). By isolating this light, the filter renders these faint structures visible against a darkened sky background.\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\u003eHigh-Contrast Views from Blocking \u0026gt;99% of Light Pollution\u003c\/h3\u003e\n\u003cp\u003eThe core function of the Optolong OIII filter is to improve contrast by aggressively rejecting unwanted light. It blocks over 99% of the primary wavelengths associated with mercury vapor, sodium vapor streetlights, and natural skyglow. This doesn't make the nebula brighter in absolute terms; it darkens the sky so severely that the nebula's faint details stand out in stark relief, transforming a washed-out view into a well-defined object.\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\u003ePrecision Optics: λ\/4 Wavefront and 60\/40 Surface Quality\u003c\/h3\u003e\n\u003cp\u003eA filter should only reveal detail, not degrade it. Optolong builds this filter on a 1.85mm optical glass substrate polished to a 60\/40 surface quality and a transmitted wavefront of λ\/4 or better. This level of optical precision ensures that the filter will not introduce aberrations or soften the image, preserving the sharpness delivered by your telescope's main optics. The multi-layer, ion-assisted coatings provide durability and resistance to scratching while ensuring wavelength stability regardless of temperature.\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\u003e18nm vs. Narrower OIII Filters: The Visual Advantage\u003c\/h3\u003e\n\u003cp\u003eWhile astrophotographers often use ultra-narrow 3nm or 7nm OIII filters, the 18nm bandpass of this Optolong filter is intentionally wider for visual astronomy. This wider window allows more photons to reach your eye, resulting in a significantly brighter and more comfortable view through the eyepiece.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrighter Image:\u003c\/strong\u003e The 18nm design prevents the image from becoming overly dim, which can happen with narrower filters, especially in telescopes under 8 inches of aperture.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMaintains Contrast:\u003c\/strong\u003e It still provides a dramatic contrast boost, making it an ideal middle ground between a broadband UHC filter and a specialized imaging filter.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBetter for More Objects:\u003c\/strong\u003e The increased brightness makes it effective on a wider range of emission nebulae, not just the very brightest planetary nebulae.\u003c\/li\u003e\n\u003c\/ul\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 objects work best with the Optolong 18nm OIII filter?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe Optolong 18nm OIII filter excels on nebulae rich in ionized oxygen. It is most effective on \u003cstrong\u003eplanetary nebulae\u003c\/strong\u003e like the Ring Nebula (M57) and the Dumbbell Nebula (M27), and \u003cstrong\u003esupernova remnants\u003c\/strong\u003e such as the Veil Nebula complex (NGC 6960\/6992). It can also enhance portions of larger emission nebulae like the Lagoon Nebula (M8).\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill the Optolong 18nm OIII filter make nebulae brighter from my city?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo, a narrowband filter cannot make an object intrinsically brighter. Its purpose is to \u003cstrong\u003eincrease contrast\u003c\/strong\u003e. It works by blocking over 99% of common light pollution sources, which makes the sky background appear much darker. This allows the faint light from the nebula to stand out more clearly, making it easier to see, but the nebula's actual brightness remains unchanged.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow will the Optolong 18nm OIII filter improve my view of the Dumbbell Nebula (M27) in my 8\" Dobsonian?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eIn an 8\" Dobsonian, the Optolong 18nm OIII filter will make a dramatic difference on M27, especially from suburban skies. The sky background will darken significantly, causing the nebula's classic \"apple core\" shape to pop with well-defined edges. You may also begin to see the fainter lobes and internal structures that are often lost in the skyglow without a filter.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the 18nm OIII filter too aggressive for viewing the Orion Nebula (M42) with a 4\" refractor?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eFor a very bright object like the Orion Nebula (M42), an 18nm OIII filter is an excellent choice. While M42 is bright enough to see without a filter, the OIII filter will isolate the intricate, wispy details in the nebula's core and wings, revealing structure that is normally overwhelmed by the nebula's own brightness. The 18nm bandpass is wide enough that the view in a 4\" scope will remain bright and engaging.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhy choose an 18nm OIII filter instead of a narrower 7nm version for visual observing?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe 18nm bandpass is specifically optimized for the human eye. Narrower filters, like 7nm or 3nm versions, are designed for CCD\/CMOS sensors and can produce an image that is too dim for satisfying visual use, particularly in smaller telescopes. The 18nm filter provides a powerful contrast boost while maintaining enough image brightness for a comfortable and detailed view.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use the Optolong 18nm OIII filter for astrophotography?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eWhile it is primarily designed for visual use, you can use the 18nm OIII for astrophotography, especially with one-shot color cameras from light-polluted areas. It provides a stronger signal and more natural star shapes than ultra-narrowband filters. However, for serious narrowband imaging from any location, a dedicated 7nm, 5nm, or 3nm OIII filter will provide higher contrast and better rejection of moonlight.\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\u003eBandpass\u003c\/td\u003e\n\u003ctd\u003e18nm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCentral Wavelength\u003c\/td\u003e\n\u003ctd\u003e500nm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSubstrate Material\u003c\/td\u003e\n\u003ctd\u003eOptical Glass\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSubstrate Thickness\u003c\/td\u003e\n\u003ctd\u003e1.85mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAverage Transmission\u003c\/td\u003e\n\u003ctd\u003e\u0026gt;80%\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBlocking Range\u003c\/td\u003e\n\u003ctd\u003e400-700nm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBlocking Depth\u003c\/td\u003e\n\u003ctd\u003e\u0026gt;99% of light pollution lines\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSurface Quality\u003c\/td\u003e\n\u003ctd\u003e60\/40\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTransmitted Wavefront RMS\u003c\/td\u003e\n\u003ctd\u003eλ\/4\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eParallelism\u003c\/td\u003e\n\u003ctd\u003e30s\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAvailable Sizes\u003c\/td\u003e\n\u003ctd\u003e1.25\" Mounted, 2\" Mounted\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\"\u003eOptolong OIII 18nm Nebula Filter (Selected Size)\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\"\u003eProtective Plastic Case\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/optolong-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eOptolong 3-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Optolong","offers":[{"title":"1.25\" Mounted","offer_id":52941926269213,"sku":"OPT-12701","price":79.0,"currency_code":"USD","in_stock":true},{"title":"2\" Mounted","offer_id":52941926301981,"sku":"OPT-12702","price":108.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Optolong-narrowband-OIII-filter-is-designed-for-nebula-observation-allowing-18nm-bandwidth-of-light-centered-on-a-wavelength-of-500nm-through-1_d6a50468-3847-45e5-a0b6-0ecabb379087.jpg?v=1789592430","url":"https:\/\/davidastro.com\/fr-us\/products\/optolong-oiii-18nm-filter","provider":"David Astro","version":"1.0","type":"link"}