SVBONY 2″ CLS Light Pollution Filter

Product Overview

The SVBONY F9155B is a 2″ CLS (City Light Suppression) filter in a standard M48 x 0.75 cell. It is a broadband light pollution filter: SVBONY specifies about 90% transmission at the main nebula emission lines (H-alpha 656 nm, OIII 496 nm, H-beta 486 nm, SII 672 nm) and about 0.1% transmission at the sodium (589 nm) and mercury (435 nm and 578 nm) lines produced by street lighting. The coated glass is 1.85 mm thick.

A CLS filter does not remove light pollution or make an object brighter. It raises the contrast between nebulae and a skyglow-brightened background, which is what makes faint structure easier to see and to stretch in processing.

Who It's For

This is a good match if you image or observe from a suburban or city-edge site with a colour astronomy camera or an unmodified DSLR and want more contrast on emission nebulae. SVBONY designs it with colour CCD/CMOS cameras and unmodified DSLRs in mind.

Key Features & Design

• Emission lines passed: about 90% transmission at H-alpha, OIII, H-beta and SII (SVBONY figures).
• Street-light lines suppressed: about 0.1% transmission at sodium 589 nm and mercury 435/578 nm.
• Hard coatings: electron-beam evaporation with ion-assisted deposition, for scratch resistance and stable performance.
• Even coating: SVBONY uses a planetary rotation system in the coating chamber for consistent passbands across the glass.
• Standard 2″ cell: M48 x 0.75 thread, 1.85 mm glass.

Recommended Uses

• Colour deep-sky imaging from light-polluted sites: emission nebulae such as M42, the Lagoon and North America Nebula.
• DSLR astrophotography: with unmodified cameras through a 2″ nosepiece or filter drawer.
• Visual observing: a darker background and better nebula contrast at sub-rural sites.

Compatibility and Accessory Notes

• Thread: M48 x 0.75, for 2″ barrels, diagonals, filter drawers and 2″ eyepieces.
• Other sizes: SVBONY also makes this filter in 1.25″ (F9155A, M28.5 x 0.6) and as a Canon EOS-C clip-in (F9155D).
• CLS vs UHC: SVBONY notes that the CLS has a wider passband than its UHC filter and suits sites with less light pollution; the UHC is the stronger choice under brighter skies.

If you want help choosing between CLS, UHC and a dual-band filter for your sky and camera, get in touch and we will work through it with you.

Good to Know Before You Order

• Broadband filters favour emission nebulae: galaxies and star clusters emit across the whole spectrum, so their gain from a CLS filter is smaller.
• Colour cast: as with any light pollution filter, images show a colour shift that is corrected in processing with a colour calibration step.
• Weight: SVBONY does not publish a weight for this filter.

Frequently Asked Questions

Is it difficult to set up?

No. It threads into any M48 x 0.75 filter thread on a 2″ nosepiece, diagonal or filter drawer.

Will it work under a dark sky?

It still passes the emission lines, but its benefit is greatest where sodium and mercury lighting brighten the background.

Does it work with a modified DSLR?

SVBONY designs it for colour cameras and unmodified DSLRs. It passes H-alpha, so it also works on a modified camera.

Can I use it for visual observing?

Yes. SVBONY lists both visual and photographic use.

Bottom Line

In short: a 2″ M48 broadband CLS filter that suppresses sodium and mercury street-light lines while passing H-alpha, OIII, H-beta and SII, raising nebula contrast for colour imaging and observing from light-polluted skies.