The Altair Dual-Band ULTRA OIII / SII narrow band filter with extremely tight 4 nm FWHM bandpass.
This filter is designed to be the perfect complement to the Altair Ha OIII 4 nm filter. By using both filters, you will get twice as much OIII data as you would otherwise, so now you can take proper Hubble palette style images with a color camera.
This filter offers what most consider to be the perfect balance between flexibility and transmission. In addition, it offers 90% transmission at both wavelengths in the same filter , thanks to a special coating process.
For imaging in moonlight and extreme light pollution situations, such as in a big city, with a color CMOS camera, or even in dark conditions if you want full control over your channels.
The filter transmits only SII and OIII light from emission nebulae, with almost total suppression of unwanted light, with OD4/5 (0.01 % ~ 0.001 %) over most unwanted visual wavelengths.
In an Altair-initiated process, each individual filter has an individual test report, unique to that particular filter, not a general test report for the entire batch.
Narrow-band bicolor imaging is a booming new trend in astrophotography, especially popular in areas with light pollution or intense moonlight. First, Altair brought you the TriBand and Quad Band filters, now we have the DualBand Ultra for the most extreme signal versus background performance.
Features of the Altair DualBand 4 nm filter:
- Capture the two main bands of emission nebulae at the same time, while suppressing light pollution, moonlight and airglow.
- More data in less time, extending the imaging window, even in the summer months when it is not yet fully dark. Capture twice as much OIII data and, at the same time, get Sii to complement the Altair Ha OIII dual band filter.
- Extremely steep bandpass produces maximum contrast in extreme light pollution conditions: 4 nm FHWM centered on the Oiii wavelength of 500.7 nm and 4 nm FHWM centered on the SII wavelength of 671.6 nm.
- Suppression of halos . We have received no reports of halos caused by this filter during testing.
- Can be used with mono or CMOS One Shot Color (OSC) astronomical cameras to obtain luminance data.
- It includes UV blocking for modified and unmodified DSLR cameras, plus an anti-reflection coating for halo suppression. To see the anti-reflective coating in action, see images showing the same filter with and without the anti-reflective coating on the Capella shining star in exactly the same conditions at the same settings.
- Best performance at focal ratios as fast as F4.8, with contrast increasing as the focal ratio increases. More information on light pollution filter performance and focal ratio here.
- The 2" filter has a standard M48x0.75mm thread and fits inside Altair magnetic filter holders, standard 2" filter wheels, plus Altair's Canon / Nikon DSLR to astro CMOS lens adapters.
Altair DualBand ULTRA 4nm Altair filter specifications:
- 1.1st band, OIII CWL500.7 nm FWHM 4 nm tolerance ~0.5 nm, T% 90% ~3% Tol.
- 2nd band, SII CWL 671.6 nm FWHM 4 nm tolerance ~0.5 nm T% 90% ~4% Tol.
- OD4/5 blocking (0.01 %~0.001 %) over most undesired wavelengths
- 1.85 mm thick optical glass with 30 arc second parallelism.
- Si02 "hard" top coat with UVIR blocking and anti-reflective coating for durability.
