Optolong UHC Ultra-High Contrast Light Pollution Filter

The UHC (Ultra-High Contrast) broadband filter is designed to improve the visibility of various deep-sky objects. By selectively reducing the transmission of wavelengths of light pollutants, specifically those produced by artificial lighting such as mercury vapor lamps, both high & low pressure sodium vapor lights and the unwanted natural light caused by neutral oxygen emission in our atmosphere (skyglow).

The filter is highly transparent in the 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 in suburban and rural areas with heavy light pollution.

Main Use and Performance

• Suitable for color CCD cameras and unmodified DSLRs that accept 1.25" filters.
•  With narrower bandpass transmission gaps, this filter provides higher contrast than CLS filters.
•  The UHC filter has a substantial red bandpass and offers superb views of 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.

Specifications

• Schott substrate material
•  Thickness 2.0 mm (1.25"/2"/36mm/77mm/82mm)
•  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 the 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, 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 from 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

Filter Cell

• Ultra-thin filter cell minimizes vignetting by maximizing the clear aperture (clear aperture is 26mm for 1.25")
•  Aerometal Material | Precise CNC Machining | Sand Blasting Process | Black Anodized Finish | Extinction Treatment to Prevent Reflection | Laser Engraving No Fading

Package

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

Size

• Standard 1.25"

• H-β486.1nm OIII 495.9nm OIII 500.7nm H-α656.3nm

• Hg 435.8nm 546.1nm 577nm 578.1nm
• Na 598nm 589.6nm 615.4nm 616.1nm