Optolong CLS 2" Mounted Filter

The Optolong CLS (City Light Suppression) 2" Mounted Filter is a broadband filter designed to enhance both visual observation and astrophotography under light-polluted skies. By selectively blocking wavelengths associated with artificial lighting—like sodium and mercury vapor emissions—it significantly improves contrast and clarity for celestial objects.

Ideal for deep-sky targets including nebulae and galaxies, this filter offers excellent transmission of key emission lines such as H-beta, OIII, H-alpha, and SII. It also helps suppress skyglow caused by naturally occurring oxygen emissions. Whether you're imaging or observing, the Optolong CLS filter provides a cleaner view of the universe with high efficiency and precision.

• Filter Type: CLS (City Light Suppression) Broadband
• Size: 50.8mm (2")
• Filter Shape: Round
• Insert Style: Threaded
• Optical Thickness: 2.0 mm
• Material: Schott B260 glass (Germany)
• Surface Quality: 60/40 (MIL-O-13830)
• Transmission Characteristics:
  • >95% at H-Beta 486nm
  • >95% at OIII 496nm / 500nm
  • >95% at H-alpha 656nm
  • >95% at SII 672nm
  • <0.1% at Hg 435nm / 578nm
  • <0.1% at Na 589nm
• Coatings: Multi-layer anti-reflection via ion-assisted deposition
• Construction: CNC-machined filter cell, black anodized, laser-engraved
• Clear Aperture: 45mm
• Use Case: Light pollution suppression for visual and imaging use

• Optolong 2" Round Mounted CLS Filter
• Protective Plastic Filter Case