Astronomik CLS filter

The Astronomik CLS filter is the best choice for observing in light-polluted areas when the targets are galaxies, gas nebulae, star clusters, or comets.

Due to its wide passband, the Astronomik CLS filter allows a lot of light to pass through, so that stars are only minimally dimmed. The filter is designed to block as much unwanted light as possible while still transmitting the maximum amount of light from astronomical objects.

The Astronomik CLS filter almost completely blocks the emission lines of high- and low-pressure vapor lamps (sodium (Na) and mercury (Hg) ), the emission maxima of LED lighting, as well as all lines of natural airglow. However, most of the light from stars and emission nebulae passes through. This significantly enhances the contrast between deep-sky objects and the background. Thanks to its design, the Astronomik CLS filter is ideal for observing a wide range of objects, including galaxies, open and globular clusters, reflection and gas nebulae as well as comets.

Other uses

The Astronomik CLS filter can also be used for photography from light-polluted areas.

Alternatives

• The Astronomik UHC filter is particularly suitable for observing emission nebulae under light pollution and dark skies.
• The Astronomik UHC-E filter is better suited for observing emission nebulae and comets under moderate light pollution.

Suitability of the Astronomik CLS filters

• Visual observation (dark skies): Rather unsuitable
• Visual observation (urban skies): Reasonable, particularly suitable for heavy light pollution

Technical Data

• 92% transmission at 486nm (H‑beta)
• 92% transmission at 496nm (OIII)
• 92% transmission at 501nm (OIII)
• 97% transmission at 656nm (H-alpha)
• Transmission range: 450 to 540nm and above 650nm
• Glass thickness: 1mm (except Astronomik OWB Type 3 and XT filters)
• Finely polished optical glass, free of any striae, residual stresses, and bubbles
• Extremely scratch-resistant and durable coating
• Completely resistant against high humidity and aging effects
• Parfocal with other Astronomik filters
• Diffraction-limited
• Optimized spectral windows
• Delivered in a high-quality, long-lasting filter box
• Made in Germany

Astronomik filters are diffraction-limited, ensuring that the optical performance (resolution and contrast) of your telescope is not compromised. Thanks to the high-precision machining of the glas substrate, all Astronomik filters are parfocal. The wedge errors are far below all common tolerances. Therefore, all issues concerning focal distances and the exact alignment of images from each color channel are effectively eliminated.

All Astronomik filters are ideal for modern cameras, including both CMOS- and CCD-based models, ensuring you capture the best possible images with your equipment. Sharpness, contrast, and the absence of any reflections and halos are guaranteed. Even with bright stars in the field of view, nebulae and galaxies will be captured with the finest structures. The Astronomik MFR and MaxFR coatings are designed for optimal performance across a wide range of focal ratios of the optics used.

Every Astronomik filter undergoes a rigorous quality control process before delivery.