Description: The H-Beta 25nm Filter allows you to visually observe the ever-popular yet elusive Horsehead Nebula with large aperture telescopes under dark skies, and can also be used to image the Horsehead as well as others that emit light at 486nm, such as the California and nebulae. Features: 1.CNC machined and black anodized aero-metal filter cell that is ultra-thin to provide largest clear aperture2.Laser-engraved to prevent fading3.Multiple layers of anti-reflection non-cementing coatings applied via electron-beam evaporation with Ion-assisted deposition4.Filter substrate is fine-optically polished to 1/4 wave and <30 parallelism over both surfaces5.Good value transmission of pass-band and optical density of off-band is assured through Optolong??s planetary rotation system, a homogenous and precise coating procedure6.Each filter comes with a plastic case with high pressure EVA case lining7.Best used with a moderate to large aperture telescope and clear, dark skies Specification: 1.Thin metal cells have a clear aperture of 26mm for 1.25 inch filters2.Blocking area: 400-700nm3.Transmittance: 80% at 486nm 4.0.1% transmission Hg at 435nm and 578nm5.0.1% transmission Na at 589nm6.FWHM: 25??3nm7.Thickness: 1.85mm8.Surface quality: 60/40 (Refer to MIL-O-13830)9.Thread Size: M28.5*0.610.Net Weight: 5.4g /0.19oz WARNING: The filters are not designed for sun observation. DO NOT LOOK AT THE SUN WITH this FILTER. You would be BLIND if you fail to observe the warning. Package includes: 1 x SV132 1.25" H-Beta Filter Details Pictures:
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