UHC Light Pollution Filter:

The UHC (Ultra High Contrast) 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 lights including mercury vapor lamps, both high and low pressure sodium vapor lights, and the unwanted natural light caused by neutral oxygen emission in our 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 and photographic purpose at sub-rural areas with heavy light pollution.

Main Use and Performance

• Suitable for color CCD cameras and unmodified DSLRs
• The UHC filter has a narrower pass-band which provides higher contrast than the CLS filter, making it is more suitable for urban environments where there is severe light pollution.
• The UHC filter has a substantial red pass-band which offers superb views for objects like the Orion Nebula (M42).
• Light pollution filters do not eliminate the effects of light pollution or increase the object’s brightness. In many cases, they increase the contrast between nebula and night sky, not brightening the nebula.
• Manufacturer's WARNING: The filters of Optolong are not designed for sun observation. DO NOT LOOK AT THE SUN WITH OPTOLONG FILTER. You would be BLIND if you fail to observe the warning.

Technical Data

• Schott substrate material
•  Thickness 2.0mm (1.25-inch, 2-inch, 36mm, 77mm, and 82mm)
•  Thickness 1.0mm (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 the both surfaces
•  95% transmission of main nebula emission lines (i.e. H-alpha is 656nm, OIII is 496nm, and 500nm, SII is 672nm, and H-beta is 486nm.
•  0.1% transmission of off-band, specifically the major emission lines of artificial light pollution (i.e. Na is 589nm, and Hg is 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.

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) no deviation affected by temperature change
• Optolong's 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 minimize vignetting by maximize possible clear aperture (clear aperture is 26mm for 1.25-inch; 45mm for 2-inch)
•  Aerometal Material, 
• Precise CNC Machining, 
• Sand Blasting Process, 
• Black Anodized Finish, 
• Extinction Treatment to Prevent Reflection, 
• Laser Engraving = No Fading

Sizes

• Standard 1.25-inch and 2-inch, Round, Mounted.

Spectral Curve

• The Major Emission Lines of Nebulae
• H-b is 486.1nm
• OIII is 495.9nm and 500.7nm
• SII is 672nm
• H-a is 656.3nm

• The Major Emission Lines of Artificial Light Pollution
• Hg is 435.8nm, 546.1nm, 577nm, and 578.1nm
• Na is 598nm, 589.6nm, 615.4nm, and 616.1nm

• UNC Light Pollution Filter