The H-alpha 7nm filter is the most popular narrowband filter allowing 7nm bandwidth of light centered on a wavelength of 656nm through, and reducing the transmission of certain wavelengths of light, specifically those produced by artificial light including mercury vapor, and both high and low pressure sodium vapor lights and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow).

Main Use and Performance

• Suitable for viewing on faint emission nebula of H-alpha line in full moonlight or in severe light pollution
• Hubble look of images can be made by the combination of H-alpha, OIII-CCD and SII-CCD, such as the famous “Pillars of Creation” (M16 Eagle Nebula)
• Narrowband imaging with SHO set (H-alpha, OIII-CCD, and SII-CCD) can be done with the moon up in heavy light pollution, so your equipment is not sitting dormant for several weeks
• H-alpha filter is the first narrowband addition to LRGB set for most imagers who blend a black-and-white Ha image into RGB data to enhance structural detail while maintaining natural look
• Narrowband filter 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.

This ultra narrowband 7nm H-alpha filter is intended to be utilized in color filter wheels that accept 31mm filter sizes.

WARNING: The filters of Optolong are not designed for sun observation. DO NOT LOOK AT THE SUN WITH OPTOLONG FILTERS. You would be BLIND if you fail to observe the warning.

Technical Data

• Technical Data Technical Data
• Schott substrate material
• Thickness 2mm
• 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
• 80-percent transmission at the h-alpha line 656nm infrared wavelength 700 to 1100nm cut-off
• 0.1-percent transmission of off-band, specifically major emission lines artificial light pollution (i.e. Na 589nm, Hg 435nm, and 578nm). Transmission of 0.1-percent is equivalent to OD3 (Optical Density), and high optical density value indicates very low transmission, and low optical density indicates high transmission.

Coating Parameter

• Non-cementing optical substrate coating
• Electron-beam gun evaporation with low 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

• H-alpha 7nm 31mm Filter
• A threaded version of this filter is pictured. Actual product is a 31mm unmounted filter
• A very narrow emission-line filter
• Permits a 7nm bandwidth of light (focused on the 656nm wavelength) through
• Blocks transmission of contrast-killing light pollution wavelengths