Optolong CLS (City Light Suppression) Filter 2"

The Optolong CLS (City Light Suppression) broadband filter is designed to improve the visibility of various deepsky objects.

By selectively reducing the transmission of wavelengths of light pollutants, specifically those produced by artificial lightings including mercury vapor lamps, both high & low pressure sodium vapor lights and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow). Together with the high transmittance in main emission lines of nebulae, namely O-III(496nm and 500nm), H-beta (486nm), N-II(654nm and 658nm), H-alpha(656nm) and S-II(672nm), the filter is suitable for enhancing the contrast and details for both visual and photograhic purpose at sub-rural area.

Main Use and Performance

Suitable for CCD cameras and DSLRs. CLS with wider pass-band than UHC and hence is more favored when observing under mild to moderate light pollution and more natural color retention. Light pollution filters neither nullify light pollution nor make nebulae brighter. In most situations, they just enhance the contrast of a nebula and reduce the background brightness. The brightness of the nebulae is not increased.

WARNING:

Optolong filters are not designed for solar observation. DO NOT LOOK AT THE SUN WITH ANY OPTOLONG FILTER as permanent eye damage will be the result.

Technical Data

• Schott substrate material
• Glass thickness 2.0 mm (1.25”/2”/36mm)  and 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. Ha 656nm, OIII 496nm & 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, and low optical density indicates high transmission.

Filter Cell

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

Available Sizes

• Standard 1.25” & 2”
• Round 36mm Unmounted
• Clip Filter Series (RESTRICTED TO GERMANY! Please do not order optolong Clip filters from Germany. We can sell only Astronomik EOS Clip filters to Germany.)

Packaging

• Plastic PP Case
• Imported High Pressure EVA Case Lining
• Silver Cardboard Box
• High Density Sponge Carton Lining

Optical Coating

• Multi-layer 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) no deviation affected by temperature change.
• Planetary rotation system offers precision and homogeneity of coatings ensuring high value on transmission of pass-band and Optical density of off-band. (Please note, "planetary rotation system" is a type of optical coating process and does not refer to the astronomical system describing the motion of the planets in our solar system.)

The Major Emission Lines of Nebulae: H-α 656.3nm, H-β486.1nm, OIII 495.9nm, OIII 500.7nm 
The Major Emission Lines of Artificial Light Pollution: Hg 435.8nm, 546.1nm, 577nm, 578.1nm, Na 598nm, 589.6nm, 615.4nm, 616.1nm