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Main Feature 2" astronomy filter with standard M48.5x0.75 male filter thread (no female thread, so it cannot be stacked with other filters). Ultra-thin filter cell to minimize vignetting; clear optical aperture of 45mm. Precision CNC-machined metal filter cell with sand blasted black anodized finish, anti-reflection treatment, and laser engraving. High quality protective plastic storage case Main Uses and Performance Suitable for enhancing the contrast and details for both visual and photographic purpose at urban and suburban areas with heavy light pollution. Suitable for color CCD cameras and unmodified DSLRs. UHC has a narrower passband and thus provides higher contrast than a CLS (City Light Pollution / Light Pollution Reduction) filter. Thus it is more suitable for urban environments where you suffer from severe light pollution. UHC has a substantial red passband and offer superb views of objects like the Orion Nebula (M42). Spectral Curve Transmission Characteristics 95% transmission of main nebula emission lines: H-beta 486.1nm, OIII 495.9nm and 500.7nm, H-alpha 656.3nm, and SII 672nm. 0.1% transmission of major transmission lines of artificial light pollution: Hg (Mercury) at 435.8nm, 546.1nm, 577nm, and 578.1nm. Na (Sodium) at 598nm, 589.6nm, 615.4nm, and 616.1nm. Technical Specifications Both surfaces are fine optically polished, accurate to 1/4 wavelength or better, and parallel to within 30 seconds or arc. 2mm thick Schott B270 optical glass substrate material. Very high surface quality of 60/40 or better (US Military Spec MIL-O-13830). Optical Coating Specifications Multi-layer anti-reflection coated. 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) so that there is no deviation due to temperature changes during use. Precise and homogeneous coatings ensure high values of desired passband and blocking of unwanted offband.

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