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IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.
Optolong CLS Light Pollution Filter
Optolong CLS Light Pollution Filter
Optolong CLS Light Pollution Filter
Optolong CLS Light Pollution Filter
Optolong CLS Light Pollution Filter
Optolong CLS Light Pollution Filter
Optolong CLS Light Pollution Filter

Optolong CLS Light Pollution Filter

par Optolong
UGC OPT-11801
$55.00 - $85.00
$55.00
$55.00 - $85.00
$55.00
Égalisation de prix!
  • Suppresses common light pollution sources
  • Average transmission greater than 90% on key nebula emission lines
  • Blocks light pollution lines with >99% efficiency
  • 1.85mm thick optical glass substrate
  • λ/4 transmitted wavefront and 30s parallelism
En rupture temporaire
Alerte de retour en stock
Info disponibilité
Admissible à la livraison GRATUITE aux USA pour les commandes de plus de 350$.
  • Description
  • FAQ
  • Specifications
  • In the Box
  • Warranty

  • Optolong CLS Light Pollution Filter

    The 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.

    Targeted Light Pollution Suppression: >99% Blocking of Sodium & Mercury Lines

    The 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.

    High-Transmission Broadband Design: >90% Pass-Through on Key Emission Lines

    While 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.

    Precision-Coated 1.85mm Glass: λ/4 Wavefront and 30s Parallelism

    Optolong 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.

    Optolong CLS vs. UHC Filters: Choosing the Right Tool for Your Sky

    The CLS is often compared to Ultra High Contrast (UHC) filters. The primary difference is the width of the passband.

    • Optolong CLS Filter: 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.
    • UHC Filter: 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.

  • What is the main difference between the Optolong CLS and a UHC filter?

    The Optolong CLS filter 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.

    Can I use the Optolong CLS filter for imaging galaxies like Andromeda (M31)?

    Yes, but with limitations. Galaxies are broadband targets, meaning they emit light across the entire visible spectrum. The Optolong CLS filter 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.

    How will the Optolong CLS filter perform on the Orion Nebula (M42) from my suburban backyard with an 8" SCT?

    The Optolong CLS filter 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.

    Is the Optolong CLS filter suitable for an unmodified DSLR camera?

    Yes, the Optolong CLS filter 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.

    Does the Optolong CLS filter make nebulae look brighter?

    No, this is a common misconception. No filter can increase an object's actual brightness. The Optolong CLS filter 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.

    Why does my Optolong CLS filter look like a mirror and change colors?

    This is normal for an interference filter like the Optolong CLS. 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.

    WARNING: Can I use the Optolong CLS filter for observing the Sun?

    Absolutely not. 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.

  • Filter Type Broadband Light Pollution Suppression (CLS)
    Available Sizes 1.25" Mounted, 2" Mounted
    Substrate Optical glass
    Thickness 1.85mm
    Average Transmission >90%
    Blocking Range 400-700nm
    Blocking Depth >99% on light pollution lines
    Transmitted Wavefront λ/4
    Parallelism 30s
    Surface Quality 60/40

    • Optolong CLS Light Pollution Filter

      × 1

    • Protective Case

      × 1

  • Optolong 3-Year Warranty