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Altair Dual-Band nebula filter for astro imaging with extreme light pollution, in the city.
This filter transmits only the H and Oiii light from emission nebulae, with almost total suppression of 99.9% OD4 on unwanted visual wavelengths.
An extremely steep bandpass yields maximum contrast in extreme light pollution: 6.5nm FHWM centred on 500.7nm Oiii wavelength, and 7nm centred on the 656.3nm Ha wavelength.
Can be used with One Shot Colour (OSC) CMOS or mono astronomical cameras for luminance data.
Includes UVIR blocking for both modified and un-modified DSLR cameras, plus an anti-reflection coating.
Best performance at focal ratios slower than F3.0, however allows use with refractor and lens based optical systems as fast as F2.0, with contrast increasing as focal ratio increases. Note: Because Dual Band is a 7nm narrowband filter, reflector telescopes with a central obstruction working at focal ratios faster than F3 may show reduced contrast in the Ha wavelengths. This due to the increased angle of incidence at the outer edge of the mirror compared to the centre forming the predominant proportion of the image, and blocking of any beneficial perpendicular rays by the central obstruction.
Narrowband Bi-Colour imaging is a growing new trend in astrophotography, especially popular in light polluted areas, or bright moonlight.
Now you can capture the two main emission nebulae bands at the same time, whilst suppressing light pollution, moonlight, and airglow. Capture more data in less time, and open up your imaging time window - even into the summer months when it isn't quite dark yet.
The 2" filter has standard M48x0.75mm thread, and fits inside the Altair Magnetic Filter holders, plus the Altair Canon / Nikon DSLR lens to astro CMOS adaptors.
Altair OSC line filters work by isolating the primary nebulae emission zones in the red and blue wavelengths, and separating them into two main "zones" with a wide separation for easy capture with a colour camera - all in one exposure! Not only is capture more convenient with one filter, but processing is easy too, thanks to the wide separation of the green/blue and red "zones". Light pollution control is extremely effective and LED light is also significantly reduced.
There are 3 types of OSC line filters in the Altair range:
Duo-Band - the allowing only the thinnest peaks of Ha 656.3nm and 500.7nm Oiii light from emission nebulae through. (Recommended for extreme light pollution in the worst possible conditions).
Tri-Band - combines Ha into a red zone, and H-beta + Oiii into a green/blue zone. (For urban light pollution).
Quad Band - combines Sii AND Ha into a red zone, and H-beta + Oiii into a green/blue zone. (For suburban / moderate light pollution).
Sensitive OSC or "One Shot Colour" CMOS cameras like the Altair Hypercam capture these wavelengths very efficiently, and allow them through the Bayer matrix. The filters also work with DSLRs (APS-C sensor size modified cameras are best, but normal ones will also work). When you have the complete stack of exposures, processing is relatively easy because of the large separation in colour. You can also use these filters as a "super luminance filter" for imaging nebulae with Mono cameras.
DUAL BAND OSC filter specifications: 1st band, Oiii CWL500.7nm FWHM 6.5nm 2nd band, Ha CWL 656.3nm FWHM 7nm 1.85mm thick optical glass with 30 arc sec parallelism. Si02 "hard" overcoat with UVIR Block and Anti-Reflection Coating.
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Recommended for the Altair 2" 7nm Dual-Band OSC Filter (Ha & Oiii)