Triband RGB Ultra II Filter 2" - Antlia

The Antlia RGB Ultra II Triple Band filter is designed to remove a good portion of light pollution for "one-shoot color" (OSC) cameras such as color astronomy cameras or digital cameras as well as monochrome cameras. Antlia offers instead of 3 distinct RGB filters: a single filter crossing these 3 spectral domains. The blue has a wide band of 20nm, the green of 25nm allowing the passage of the OIII lines (at 495.9 and 500.7nm) and the red of approximately 30nm (with the passage of the NII, H-Alpha and SII lines) .

It is therefore more selective than classic RGB filters which do not cut light pollution... while being more "bright" than H-Alpha, SII, OIII type interference filters. It is therefore compatible with the imaging of galaxies and clusters (which radiate throughout the visible spectrum). Antlia estimates that 90% of objects are photographable in a sky between 1 and 8 on the Bortle scale... with a balanced and particularly well-crafted color balance. Another important aspect of this particular filter is a clear "cut-off" of each zone and compatibility with instruments with an ultra-short focal ratio up to f/2.

This version II offers 2 important improvements. The first is a higher transmission rate in the 3 spectral zones (except a slight loss in SII), an appreciable plus for the search for maximum brightness/contrast. The second is a shift in the central spectral band. The H-Beta and OIII lines are better covered as shown in the curve below.

Applications and performance

• Designed specifically for use with color DSLR, CMOS and CCD cameras and monochrome sensors. Removing optical density (OD) 4 on unwanted visual wavelengths increases the signal-to-noise ratio
• For imaging nebulae, galaxies and star clusters... and visual observation of the deep sky (on large diameter telescopes > 250mm)
• Clean cuts of extremely steep lines minimize internal reflections
• Ion gun-assisted deposition coating technology on the double-sided polished substrate, making it the most consistent and precise light pollution suppression filter
• Good performance at focal ratios above F/2, with contrast increasing with focal ratio
• Designed to suppress a significant portion of artificial lighting from Bortle scale 1 to 8. Near IR (NIR) is blocked up to 1100nm
• Transmission rate greater than 94% for H-Alpha, SII, NII, OIII lines
• 2" (50.8mm) sinking screwed to M48 pitch