Compact CLS Filter for Astronomical Photography

The City Light Suppression broadband filter, designed by the brand SVBONY, aims to enhance the visibility of various deep-sky objects. This filter selectively reduces the transmission of wavelengths associated with light pollution, including those emitted by mercury vapor lamps, high and low-pressure sodium vapor lights, and the unwanted natural light caused by neutral oxygen emission in the atmosphere, such as sky glow.

The filter's manufacturing process involves precise CNC machining, sand blasting, and black anodized finish to prevent reflection and laser-based extinction treatment. The planetary rotation system ensures precision and homogeneity of the coatings, resulting in high transmission of the pass-band and high optical density of the off-band.

With a 90% transmission of the main nebula emission lines (Ha 656nm, OIII 496nm & 500nm, SII 672nm, and H-beta 486nm), and only 0.1% transmission of the major emission lines of artificial light pollution (Na 589nm, Hg 435nm and 578nm), the CLS filter is well-suited for both visual and photographic deep-sky observation in sub-rural areas affected by mild to moderate light pollution.

Unlike filters that merely eliminate the effects of light pollution or increase the object's brightness, the CLS filter enhances the contrast between the nebula and the night sky, without directly brightening the nebula. This makes it a favored choice over the UHC filter when observing under such conditions.

Constructed with an optical glass lens and an aluminum frame, the CLS filter is compatible with color CCD cameras and unmodified DSLRs. The ultra-thin filter cell design minimizes vignetting, while the engraved "CLS" marking ensures no fading over time.

It is important to note that the SVBONY filters are not designed for sun observation, and users should never look directly into the sun with these filters, as it may result in eye damage.

Overall, the CLS filter from SVBONY is a valuable tool for deep-sky observation and astrophotography, effectively enhancing the contrast and details of various nebulae and other celestial objects in areas affected by light pollution.

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