{"product_id":"optolong-cls-filter","title":"Optolong CLS Light Pollution Filter","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eSuppresses common light pollution sources\u003c\/li\u003e\n\u003cli\u003eAverage transmission greater than 90% on key nebula emission lines\u003c\/li\u003e\n\u003cli\u003eBlocks light pollution lines with \u0026gt;99% efficiency\u003c\/li\u003e\n\u003cli\u003e1.85mm thick optical glass substrate\u003c\/li\u003e\n\u003cli\u003eλ\/4 transmitted wavefront and 30s parallelism\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\u003eOptolong CLS Light Pollution Filter\u003c\/h2\u003e\n\u003cp\u003eThe Optolong CLS (City Light Suppression) filter restores contrast to your deep-sky views by blocking over 99% of common artificial light sources. Built on a 1.85mm optical glass substrate, it maintains a λ\/4 transmitted wavefront for sharp images while delivering over 90% transmission of critical nebula emission lines like H-alpha and OIII. With 30s parallelism, the filter introduces no optical distortions, making it a powerful tool for visual observers and imagers using color cameras or unmodified DSLRs under 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\u003eTargeted Light Pollution Suppression: \u0026gt;99% Blocking of Sodium \u0026amp; Mercury Lines\u003c\/h3\u003e\n\u003cp\u003eThe core function of the Optolong CLS is to surgically remove the wavelengths associated with common streetlights. It achieves greater than 99% blocking of mercury vapor, high-pressure sodium, and low-pressure sodium vapor lamp emissions. This aggressive rejection of unwanted light darkens the sky background significantly, allowing the faint signal from your target to stand out in much higher contrast.\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-Transmission Broadband Design: \u0026gt;90% Pass-Through on Key Emission Lines\u003c\/h3\u003e\n\u003cp\u003eWhile blocking unwanted light, the CLS filter maintains an average transmission of over 90% for the most important deep-sky wavelengths. This wide passband includes hydrogen-alpha (656nm), hydrogen-beta (486nm), oxygen-III (496nm and 500nm), and sulfur-II (672nm). By preserving the light from these emission nebulae, the filter reveals more detail and structure in objects like the Orion Nebula (M42) or the Lagoon Nebula (M8) without significantly altering natural star colors.\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-Coated 1.85mm Glass: λ\/4 Wavefront and 30s Parallelism\u003c\/h3\u003e\n\u003cp\u003eOptolong constructs the CLS filter from a 1.85mm thick slab of fine optical glass, ensuring mechanical stability and optical purity. Ion-assisted deposition coatings provide durability and prevent the central wavelength from shifting with temperature changes. The filter is polished to a transmitted wavefront of λ\/4 and a parallelism of 30 arcseconds, guaranteeing that it will not degrade the resolution of your telescope's optics.\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\u003eOptolong CLS vs. UHC Filters: Choosing the Right Tool for Your Sky\u003c\/h3\u003e\n\u003cp\u003eThe CLS is often compared to Ultra High Contrast (UHC) filters. The primary difference is the width of the passband.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eOptolong CLS Filter:\u003c\/strong\u003e Features a wider passband, making it more effective in mild to moderate light pollution. It preserves more natural star color and is a better general-purpose filter for a mix of objects, including reflection nebulae and star clusters.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUHC Filter:\u003c\/strong\u003e Has a narrower passband, primarily focused on the H-beta and OIII lines. This provides more aggressive contrast on emission nebulae but can dim stars more significantly. It is often preferred for darker sites or areas with more severe light pollution where maximum rejection is needed.\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 is the main difference between the Optolong CLS and a UHC filter?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe \u003cstrong\u003eOptolong CLS filter\u003c\/strong\u003e has a wider bandpass, making it a \"broadband\" filter ideal for mild to moderate light pollution. It passes more of the visible spectrum, resulting in more natural star colors. A UHC filter is a \"narrowband\" filter with a tighter passband, offering higher contrast on emission nebulae but at the cost of dimming stars more, making it better suited for more heavily light-polluted skies.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use the Optolong CLS filter for imaging galaxies like Andromeda (M31)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, but with limitations. Galaxies are broadband targets, meaning they emit light across the entire visible spectrum. The \u003cstrong\u003eOptolong CLS filter\u003c\/strong\u003e will increase the contrast between the galaxy and the skyglow, but it will also block some of the galaxy's own light. It can help bring out H-II regions in the spiral arms but may reduce the overall brightness of the galactic core.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow will the Optolong CLS filter perform on the Orion Nebula (M42) from my suburban backyard with an 8\" SCT?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe \u003cstrong\u003eOptolong CLS filter\u003c\/strong\u003e is an excellent choice for this scenario. M42 is rich in hydrogen-alpha and oxygen-III emissions, which the filter transmits with over 90% efficiency. In your 8\" SCT, the filter will dramatically darken the suburban sky background, making the faint outer loops of the nebula visible and enhancing the contrast and detail within the Trapezium region.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the Optolong CLS filter suitable for an unmodified DSLR camera?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, the \u003cstrong\u003eOptolong CLS filter\u003c\/strong\u003e is designed to work very well with color CMOS\/CCD cameras and unmodified DSLRs. Its passband includes the critical 656nm H-alpha line, which standard DSLRs are less sensitive to but still capture. The filter helps isolate this important wavelength from light pollution, improving the signal in your images.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eDoes the Optolong CLS filter make nebulae look brighter?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo, this is a common misconception. No filter can increase an object's actual brightness. The \u003cstrong\u003eOptolong CLS filter\u003c\/strong\u003e works by increasing the *contrast* between the nebula and the night sky. It achieves this by selectively blocking light pollution, which makes the background darker, thereby making the nebula easier to see against it.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhy does my Optolong CLS filter look like a mirror and change colors?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThis is normal for an interference filter like the \u003cstrong\u003eOptolong CLS\u003c\/strong\u003e. The highly reflective appearance is due to the dielectric coatings that are precisely layered to reject specific wavelengths of light. The color will appear to shift depending on the viewing angle and ambient light, which is a sign that the coatings are functioning as designed.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWARNING: Can I use the Optolong CLS filter for observing the Sun?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003e\u003cstrong\u003eAbsolutely not.\u003c\/strong\u003e The Optolong CLS filter is NOT a solar filter and is not designed for sun observation. Looking at the Sun with this filter, or any filter not explicitly designed for safe solar viewing, will cause immediate and permanent blindness.\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\u003eBroadband Light Pollution Suppression (CLS)\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\u003ctr\u003e\n\u003ctd\u003eSubstrate\u003c\/td\u003e\n\u003ctd\u003eOptical glass\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eThickness\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;90%\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% on light pollution lines\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTransmitted Wavefront\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\u003eSurface Quality\u003c\/td\u003e\n\u003ctd\u003e60\/40\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 CLS Light Pollution 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\"\u003eProtective 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\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":52941921288477,"sku":"OPT-11801","price":77.0,"currency_code":"CAD","in_stock":true},{"title":"2\" Mounted","offer_id":52941921321245,"sku":"OPT-11802","price":119.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Optolong-CLS-City-Light-Suppression-broadband-filter-is-designed-to-improve-the-visibility-of-various-deepsky-objects-1_1622ccd9-042b-4aec-b31c-a974b2ff5095.jpg?v=1789592400","url":"https:\/\/davidastro.com\/fr\/products\/optolong-cls-filter","provider":"David Astro","version":"1.0","type":"link"}