Optolong H-alpha 7nm 2″ Filter
The Optolong H-alpha 7nm is a premium narrowband filter for nebula astrophotography. It passes light at a central wavelength of 656.3 nm with a bandwidth of just 7 nm - matching the characteristic emission line of hydrogen H-alpha. This extremely narrow passband blocks unwanted light from artificial sources and natural atmospheric glow, so you can photograph deep-sky objects even from heavily light-polluted locations.
Why Choose a 7nm H-alpha Filter?
The H-alpha 7nm narrowband filter is one of the most popular filters among astrophotographers worldwide. It dramatically reduces transmission of wavelengths produced by mercury vapour lamps, low- and high-pressure sodium lamps, and urban LED lighting. At the same time, it eliminates the natural emission of neutral oxygen in the Earth's atmosphere - known as skyglow - which otherwise reduces contrast in images taken from suburban sites.
Emission nebulae such as the Orion Nebula, the Rosette Nebula, and the California Nebula emit a large portion of their light in the H-alpha line. The tight 7nm passband delivers high contrast between the object and the sky background, revealing fine structural details that would otherwise be lost in a bright, washed-out background.
Compatible with Colour and Monochrome Cameras
The Optolong H-alpha filter for nebula astrophotography works with both monochrome and colour cameras. In combination with a CCD or CMOS sensor, it produces exceptional results even at shorter exposure times. It is a popular choice for beginners and experienced astrophotographers alike.
Precision Optics and Robust Construction
The optical element is manufactured to a surface accuracy of 1/4 wavelength, ensuring minimal wavefront distortion and consistent sharpness across the entire field of view. The aluminium 2″ frame threads directly into a standard eyepiece holder, camera adapter, or filter wheel, and is compatible with the vast majority of telescopes and cameras on the market.
The clear aperture of 45 mm provides sufficient illumination of the imaging sensor, even with telescopes of shorter focal length. The aluminium frame is both lightweight and durable, so it adds no unnecessary stress to the telescope's mechanical components.
A multi-layer anti-reflection coating delivers 85% transmission in the target passband while minimising ghosting and flare, even when imaging bright star fields. The filter is suitable for direct use with a telescope as well as for inclusion in planetary and deep-sky filter wheels.
Technical Specifications
| Parameter |
Value |
| Filter type |
Narrowband H-alpha |
| Central wavelength |
656.3 nm |
| Bandwidth (FWHM) |
7 nm |
| Peak transmission |
85% |
| Clear aperture |
45 mm |
| Frame size |
2″ threaded |
| Frame material |
Aluminium |
| Surface accuracy |
1/4 wavelength |
| Camera compatibility |
Monochrome and colour CCD/CMOS |
What Can You Photograph with This Filter?
- Emission nebulae - Orion Nebula, Rosette Nebula, California Nebula, and many more
- Supernova remnants with hydrogen emission
- HII regions and star-forming clouds
- Any deep-sky object that emits strongly in the H-alpha line
Who Is This Filter For?
The Optolong H-alpha 7nm is the ideal choice for any astrophotographer who wants dramatically high-contrast images of emission nebulae and wishes to reveal their finest filamentary structure. Whether you are photographing from a dark-sky site or a light-polluted suburb, this filter will significantly improve the quality of your astrophotos and take your astrophotography to the next level.
Compatibility and Use
The filter is supplied in a standard 2″ threaded mount, compatible with eyepiece holders, camera adapters, and filter wheels used in amateur astronomy. It fits directly into most telescope focusers and camera nosepieces without any additional adapters. It is equally at home in a dedicated deep-sky imaging rig or a simpler beginner setup.
