Astronomik Filters CLS 50x50mm filter, unmounted (52918)

The Astronomik CLS is an affordable filter designed for visual observation, black-and-white photography, and CCD imaging of nebulae, galaxies, and star clusters. It works with astronomical instruments of any size. Since 2008, the filter has been redesigned to be "halo-free," addressing issues like reflections and halos.

Light Pollution Reduction
This filter effectively blocks light from mercury and sodium-vapor lamps while allowing most visible light and H-alpha emissions to pass. It ensures that all important emission lines, as well as the spectral range visible to dark-adapted eyes, can pass through.

Optimized Performance
The CLS filter is best suited for aperture ratios ranging from 1:3 to 1:15. Issues like transmission losses and chromatic distortions are minimal unless used with extremely bright aperture ratios (e.g., 1:2 or more). It is compatible with telescopes of all aperture sizes.

Applications

• Visual Observation: Reduces light pollution effectively in dark skies. For urban environments, UHC or UHC-E filters may be better alternatives.
• Photography:
  • Film photography: Excellent color balance.
  • DSLR photography (standard): Enhanced contrast but with a shifted color balance.
  • DSLR photography (astro-modified): Near-perfect color balance.

Technical Specifications

• Transmission:
  • 92% at 486nm (H-beta)
  • 92% at 496nm (OIII)
  • 92% at 501nm (OIII)
  • 97% at 656nm (H-alpha)
• Wavelength Range: Passes light from 450–540nm and beyond 650nm.
• Build Quality: Aluminium frame with a glass thickness of 1mm. Resistant to humidity, scratches, and aging effects.

The Astronomik CLS filter is diffraction-limited, ensuring no reduction in optical performance, and comes in various sizes and formats for different needs.