Optolong CLS Light Pollution Filter

Now: £29.60 (Save: £7.40) Was: ~~£37.00~~✓ 2 year warranty

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1.25" Mounted: £29.60
2" Mounted: £45.60
EOS-C: £52.00
EOS-FF: £63.20

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About this product

Model: opt_cls_1.25
Part Number: 11801

City Light Suppression (CLS) Filter - Block Common Light Pollution Sources

The CLS (City Light Suppression) broadband filter is designed to improve the visibility of various deep-sky objects by selectively reducing the transmission of wavelengths of light pollutants, especially those produced by artificial lighting, including mercury vapour lamps, both high and low-pressure sodium vapour lights, and light caused by neutral oxygen emission in the atmosphere (i.e. skyglow).

Together with the highly transparent in main nebula emission lines at OIII (496nm and 500nm), H-beta (486nm), NII (654nm and 658nm), H-alpha (656nm) as well as SII (672nm), the filter is suitable for enhancing the contrast and details for both visual astronomy and astrophotography.

IMPORTANT: Filters manufactured by Optolong are NOT designed for observing or photographing the Sun. DO NOT use Optolong filters to observe or photograph the Sun. If you do, it will result in permanent eye damage!

FEATURES

95% transmission of main nebula emission lines (i.e. H-alpha 656nm, OIII 496nm and 500nm, SII 672nm and H-beta 486nm
0.1% transmission of off-band, specifically the major emission lines of artificial light pollution (i.e. Na 589nm, Hg 435nm and 578nm)
Suitable for use with colour CCD and CMOS cameras and unmodified DSLRs
Wider pass-band than UHC filter - Better suited for mild/moderate light pollution
1.25" or 2" Mounted Sizes, EOS-C, EOS-FF and Nikon-FF Clip filters.
Supplied in a protective plastic case with EVA foam lining
1mm (Clip Filters) or 2mm (1.25" / 2") Thick Schott Glass
Fine-optically polished on both sides - ensures accurate λ/4 wavefront and <30 seconds parallelism over the both surfaces

Transmission Chart

Red Line - Represents the transmission curve of the CLS Filter.

Green Line - The Major Emission Lines of Nebulae: H-α (656.3nm), H-β (486.1nm), OIII (495.9nm) and OIII (500.7nm)

Orange Line - The Major Emission Lines of Artificial Light Pollution: Hg / Mercury (435.8nm, 546.1nm, 577nm and 578.1nm), Na / Sodium (598nm, 589.6nm, 615.4nm and 616.1nm)

Technical Data

Schott substrate material
Thickness 2.0 mm (1.25”/2”/36mm)
Thickness 1.0 mm (Clip series)
Surface Quality: 60/40 (Refer to MIL-O-13830)
Fine-optically polished to ensure accurate 1/4 wavefront and <30 seconds parallelism over both surfaces
95% transmission of main nebula emission lines (i.e. H-alpha 656nm, OIII 496nm and 500nm, SII 672nm and H-beta 486nm
0.1% transmission of off-band, specifically the major emission lines of artificial light pollution (i.e. Na 589nm, Hg 435nm and 578nm). Transmission of 0.1% is equivalent to OD3 (Optical Density), and a high optical density value indicates very low transmission, while a low optical density indicates high transmission.

Coating Parameter

Multi-layers anti-reflection coating
Non-cementing optical substrate coating
Electron-beam gun evaporation with Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL (central wavelength) and no deviation from temperature change
The planetary rotation system offers precision and homogeneity of coatings, ensuring high value on transmission of pass-band and Optical density of off-band

Filter Cell

Ultra-thin filter cell minimises vignetting by maximising possible clear aperture (clear aperture is 26mm for 1.25”; 45mm for 2”)
Aerometal Material | Precise CNC Machining | Sand Blasting Process | Black Anodised Finish | Extinction Treatment to Prevent Reflection | Laser Engraving No Fading