Altair Dual-Band 4.5nm CERTIFIED CMOS Nebula Filter 2" with test report

Altair SKU: F200DB4.5NM


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Altair Dual-Band Oiii / Ha nebula filter with high resolution spectrographic test report.

This filter allows astro imaging in extreme light pollution, for example in a major city, with a colour CMOS camera. 

Each individual filter has a serial number and comes with corresponding test certificate showing the bandpass, tested on a 0.1nm resolution spectrograph, our guarantee of a true 4.5nm bandpass. These are limited in quantity, and are the highest specification filter available at this time. They are made in small numbers, and you can order your individual filter online.

Narrowband Bi-Colour imaging is a growing new trend in astrophotography, especially popular in light polluted areas, or bright moonlight. First we brought you the TriBand and Quad Band filters, now we have the Dual Band for the most extreme light pollution suppression.

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.

This filter transmits only the H and Oiii light from emission nebulae, with almost total suppression of unwanted light, with OD4/5 (0.01%~0.001%) over the majority of unwanted visual wavelengths. 

  • An extremely steep bandpass yields maximum contrast in extreme light pollution: 4.5nm FHWM centred on 500.7nm Oiii wavelength, and 4.5nm FHWM 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 as fast as F4.8, with contrast increasing as focal ratio increases. Faster than F3 requires an Altair Pre-Shifted filter (please get in touch for more info). More info about light pollution filter performance and focal ratio here.

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 narrowband 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.

What does "Dual Band£" mean?

There are 3 types of OSC line filters in the Altair range:

  1. Dual-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).
  2. Tri-Band - combines Ha into a red zone, and H-beta + Oiii into a green/blue zone. (For urban light pollution).
  3. Quad Band - combines Sii AND Ha into a red zone, and H-beta + Oiii into a green/blue zone. (For suburban / moderate light pollution).
  Dual Band TriBand QuadBand
H-alpha 656.3nm Y Y Y
Oiii 500.7nm Y Y Y
Oiii 495.9nm   Y Y
Sii 672nm      Y
  2x Bands 3x Bands 4x Bands

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.

Filter technical specifications:
1st band, Oiii CWL500.7nm FWHM 4.5nm tolerance ~0.5nm
2nd band, Ha CWL 656.3nm FWHM 4.5nm tolerance ~0.5nm
OD4/5 Blocking (0.01%~0.001%) over the majority of unwanted visual wavelengths
1.85mm thick optical glass with 30 arc sec parallelism.

Si02 "hard" overcoat with UVIR Block and Anti-Reflection Coating for durability.

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