Astronomik CLS CCD Filter – Light Pollution Suppression

Overview

The Astronomik CLS CCD filter is designed for astrophotography from locations affected by artificial light pollution. It is optimised for CCD and infrared-sensitive cameras, significantly increasing contrast in deep-sky images while preserving natural star colours.

Thanks to its wide transmission range, a large amount of useful astronomical light passes through the filter, ensuring stars are only minimally dimmed while the sky background is effectively darkened.

Key Benefits

• Enhances contrast between deep-sky objects and the sky background
• Strong suppression of common artificial light sources
• Wide passbands allow high signal throughput
• Integrated IR blocking layer for CCDs, DSLRs, and webcams
• Minimal star dimming with no loss of fine detail

Optical Performance

The CLS CCD filter blocks the emission lines of low- and high-pressure mercury (Hg) and sodium (Na) lamps as well as airglow, while allowing all key astronomical emission lines to pass through.

Important emission lines such as H-alpha, H-beta, and OIII are transmitted at very high efficiency, resulting in improved nebula contrast and a darker background sky.

The integrated IR-blocking layer makes this filter ideal for:

• CCD cameras
• Astro-modified DSLR cameras
• Webcams and cameras without built-in IR filters

Telescope Compatibility

• Suitable for all telescope apertures
• Optimised for focal ratios from f/2 to f/15
• Homofocal with all Astronomik filters (except XT versions)

Usage Notes

• As a camera clip filter, DSLR imaging is possible even under extreme light pollution without damaging colour balance
• Available in 1.25″ and 2″ versions for imaging and visual observation
• If an IR-cut filter is already present in the imaging train, the standard CLS filter may be a more economical alternative

Suitability Guide

• Visual Observation (Rural): Good (depending on mercury vapour lighting)
• Visual Observation (Urban): Neutral – a UHC-E or UHC filter is more appropriate
• CCD Astrophotography: Very good – optimal suppression of light pollution
• DSLR Astrophotography (Unmodified): Good – colour shift with improved contrast
• DSLR Astrophotography (Astro-modified): Very good – excellent white balance
• DSLR (Converted with MC Clear Glass): Very good – excellent white balance
• Webcam / Video (Planets): Unsuitable
• Webcam / Video (Deep Sky): Very good when light pollution is severe

Technical Specifications

• ~95% transmission at 486nm (H-beta)
• ~95% transmission at 496nm (OIII)
• ~95% transmission at 501nm (OIII)
• ~97% transmission at 656nm (H-alpha)
• Passband 1: 450–520nm
• Passband 2: 640–690nm
• Filter thickness: 1mm
• Hard-coated, optically polished special glass
• Moisture-resistant, non-aging, scratch-resistant
• No halos and no internal reflections
• Supplied in a durable protective storage box