A. About Optolong's H-alpha (12nm) Filter
The Optolong H-alpha (Hydrogen-alpha) narrowband filter is designed to improve the visibility of various deep sky objects. It does this by:
- Selectively reducing the transmission of wavelengths of light pollutants, specifically those produced by artificial lighting (including mercury vapor lamps, both high & low pressure sodium vapor lights, and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow)).
- Allowing 12nm bandwidth of light centered on a wavelength of 656nm to pass through.
The narrowband H-alpha astrophotography filter provides very high contrast to reveal subtle nebula details.
B. Main Uses and Performance
- Suitable for viewing faint emission nebula in the H-Alpha line, even in full moonlight or in severe light pollution.
- Narrowband imaging with SHO (S-II, H-alpha, and O-III) set can be done with the moon up in heavy light pollution, so your equipment is not sitting dormant for several weeks.
- Hubble look of images can be made by the combination of H-alpha, OIII-CCD and SII-CCD images, such as the famous "Pillars of Creation" (M16 Eagle Nebula).
- H-alpha filter is the first narrowband addition to the LRGB set for most imagers who blend a black-and-white Ha image into RGB data to enhance structural detail while maintaining a natural look.
C. Spectral Curve Transmission Characteristics
- 90% transmission at H-alpha line 656nm
- 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.
- It also blocks out infrared wavelengths (700-1100nm) so a separate IR cut-off filter is not required for imaging applications.
D. 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).
E. 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.
- Every single filter is tested and passed by Optolong before shipping to dealers.
- 2" astronomy filter with standard M48x0.75 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.
WARNING: Optolong filters are not designed for direct solar observation. NEVER use these filters for observing the Sun, or permanent eye and equipment damage will result.
Aug 21, 2017
Excellent FilterPros: Cons: Comments:
I purchased this 12nm H-a filter for use with a night vision monocular to reveal the myriad nebulae in the Milky Way at 1x, 3x, and 14x at my semi-dark site. It provides a spectacular image of H-a emission lines allowing direct vision (similar to photographic quality images) of the Lagoon, Eagle, Cats Paw, North American, Pelican and many other very large nebulae. I'm very happy with this filter used for this purpose at my dark site (commonly having magnitude 5.5 skies). Even from my light polluted city, this filter helps to see these same nebulae, but either my 7nm or 5nm H-a filters are better under light polluted skies. But at the dark site, the 12nm provides a cleaner image with stars that are not attenuated like the 5 & 7nm filters. This filter also has a thinner housing (lower height profile) than some, allowing use in all filter wheels. Very satisfactory performance, excellent quality, no visible defects in the ion deposition coatings which seem very sturdy (I've cleaned it twice). Highly recommended for this type of observing.
This review was provided courtesy of AgenaAstro.comSort by