This filter delivers what most consider to be the perfect balance of flexibility and transmission. What's more it delivers 90% transmission over both wavelengths in the same filter, due to a special coating process.

For imaging in moonlight and extreme light pollution as in a major city, with a colour CMOS camera - or even in dark conditions if you want total control over your channels.

The filter transmits only the Sii 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.

In a process pioneered by Altair, each individual filter has an individual test report, unique to that particular filter, not a blanket test report for the whole batch.

Narrowband Bi-Colour imaging is a growing new trend in astrophotography, especially popular in light polluted areas, or bright moonlight. First, Altair brought you the TriBand and Quad Band filters, now we have the DualBand Ultra for the most extreme signal vs. background performance.

Altair 4nm DualBand ULTRA Filter Specifications:

• 1st band, Oiii CWL500.7nm FWHM 4nm tolerance ~0.5nm, T% 90% ~3% Tol.
• 2nd band, Sii CWL 671.6nm FWHM 4nm tolerance ~0.5nm T% 90% ~4% Tol.
• OD4/5 Blocking (0.01%~0.001%) over the majority of unwanted wavelengths
• 1.85mm thick optical glass with 30 arc sec parallelism.
• Si02 "hard" overcoat with UVIR Block and Anti-Reflection Coating for durability.