Reduces skyglow from artificial and natural light pollution Blocks >99% of mercury vapor and sodium vapor light Passes key nebula emission lines including H-Alpha, H-Beta, and OIII Transmitted Wavefront RMS of ¼ λ Available in 1.25" and 2" mounted sizes, plus DSLR clip-in formats Description FAQ Specifications Warranty Optolong UHC Filter The Optolong UHC (Ultra High Contrast) Filter is engineered to reclaim night sky views from light-polluted areas, delivering >99% blocking of artificial light sources across a 300-700nm range. By isolating critical nebula emission lines with a precision ¼ λ transmitted wavefront, it dramatically increases the contrast between your target and a brightened sky background. The entire optical system maintains 30s parallelism, ensuring the enhanced view is not distorted. UHC Suppression: >99% Light Pollution Blocking at OD3 The UHC filter aggressively targets the most common sources of urban skyglow. It achieves an optical density of OD3, blocking more than 99% of light from mercury vapor lamps, high and low-pressure sodium vapor lights, and the natural skyglow caused by neutral oxygen emission. This selective blocking darkens the sky background significantly, making faint nebula structures visible where they would otherwise be lost in the glare. Targeted Transmission: High Contrast on OIII, H-Beta, and H-Alpha Nebulae While blocking unwanted light, the Optolong UHC filter maintains high transmission for the most important deep-sky wavelengths. It passes the light from emission nebulae at OIII (496nm, 500nm), H-Beta (486nm), and H-Alpha (656nm). This makes it exceptionally effective on targets like the Orion Nebula (M42) and the Lagoon Nebula (M8), revealing intricate detail and structure by separating the nebula's light from the washed-out sky. Optical Precision: ¼ λ Wavefront and 60/40 Surface Quality A filter is only as good as the image it passes. The Optolong UHC is built on an optical glass substrate polished to a surface quality of 60/40 and a transmitted wavefront of ¼ λ or better. Ion-assisted deposition coatings ensure durability and resistance to scratching, while a 30s parallelism guarantees that you are not introducing optical errors into your imaging or visual train. This preserves the sharpness and resolution of your telescope. Optolong UHC vs. CLS: Choosing the Right Filter for Your Sky The Optolong UHC has a narrower bandpass compared to a City Light Suppression (CLS) filter, giving it higher contrast. This makes the UHC a better choice for observers in more heavily light-polluted urban and suburban environments. A CLS filter provides a more natural color balance and works well in darker locations, while the UHC excels at digging faint emission nebulae out of the most challenging skyglow. UHC Filter: Best for severe light pollution, maximizing contrast on emission nebulae. CLS Filter: Better for mild light pollution or dark sites, offering a broader passband and more natural star colors. What is the main difference between the Optolong UHC filter and a CLS filter? The primary difference is the width of the passband. The Optolong UHC (Ultra High Contrast) filter has a narrower passband, providing more aggressive light pollution rejection and higher contrast on emission nebulae. A CLS (City Light Suppression) filter has a broader passband, resulting in more natural star colors but less intense contrast, making it better suited for moderately light-polluted skies. How will the Optolong UHC filter improve my view of the Orion Nebula (M42) from a city? From a city, the Orion Nebula (M42) often appears as a small, bright core with its fainter outer structures washed out by skyglow. The Optolong UHC filter blocks this skyglow while passing the nebula's own H-Alpha, H-Beta, and OIII light. This darkens the background sky, dramatically increasing contrast and allowing you to see the faint, extended wings and intricate dust lanes of the nebula that were previously invisible. Is the Optolong UHC filter suitable for astrophotography with a color camera or DSLR? Yes, the Optolong UHC filter is designed for both visual use and astrophotography with color cameras, including unmodified DSLRs and dedicated one-shot-color astronomy cameras. Its substantial red passband allows it to capture critical H-Alpha data, which is often weak in other light pollution filters, leading to more balanced and detailed nebula images from the city. Does the Optolong UHC filter make galaxies and star clusters brighter? No. The Optolong UHC filter works by selectively blocking light, which means it will dim all objects to some degree. It is designed for emission nebulae, which emit light at specific wavelengths the filter passes. Broadband targets like galaxies, reflection nebulae, and star clusters emit light across the entire spectrum. The filter will block much of their light, making them appear dimmer and often harder to see. For these objects, it's best to observe from a dark site without a filter. Can I use the Optolong UHC filter for visual observing with my 8" Dobsonian? Absolutely. An 8" Dobsonian is an excellent instrument for visual deep-sky observing, and the Optolong UHC filter is a perfect accessory for it, especially from suburban skies. It will significantly enhance views of emission nebulae like the Swan Nebula (M17) and the Veil Nebula (NGC 6960), making them stand out clearly against a darkened sky background. Why is the Optolong UHC filter not recommended for solar observing? WARNING: NEVER use this filter for solar observation. The Optolong UHC filter is designed to block specific, narrow wavelengths of light from artificial sources at night. It does not block the intense, full-spectrum visible and invisible (infrared, ultraviolet) radiation from the Sun. Looking at the Sun with this filter, or any filter not explicitly designed for solar viewing, will cause immediate and permanent blindness. Substrate Optical glass Blocking Range 300-700nm Blocking Depth OD3, light pollution line blocking >99% Surface Quality 60/40 (MIL-O-13830A) Transmitted Wavefront RMS ¼ λ Parallelism 30s Available Formats 1.25" Mounted, 2" Mounted, Clip for Canon EOS APS-C, Clip for Canon EOS Full Frame, Clip for Nikon Full Frame Optolong 3-Year Warranty
