Askar Colour Magic C 2" Duo-Band Filter Package (C1 Hα+OIII and C2 SII+OIII)

Hubble-palette nebula images from a color camera, with two filters

The Askar Colour Magic C 2" Duo-Band Filter Package pairs two 2" mounted dual-band filters made for color astronomy cameras: the C1 (Hα + OIII) and the C2 (SII + OIII). Each one passes two emission lines and blocks almost everything else, which darkens the sky background and brings out the structure of emission nebulae. Used together, they give a color camera the three narrowband channels a mono camera gets from separate Hα, OIII and SII filters, and the set costs less than buying the two filters separately.

Key specs: C1: Hα 656.6nm (15nm FWHM) + OIII 500.7nm (35nm FWHM) · C2: SII 672nm (15nm FWHM) + OIII 500.7nm (35nm FWHM) · 90% peak transmission · OD3 blocking from 200 to 1000nm · 2mm thick glass, 60/40 surface quality · 2" mounted cells

What you can image

• Bright emission nebulae: the Orion Nebula, the Lagoon and Trifid Nebulae, the Eagle Nebula and its Pillars, and the Rosette Nebula.
• Large, faint nebula complexes: the Heart and Soul Nebulae (Askar's sample shows the Soul Nebula, IC 1848), the North America and Pelican Nebulae, and the Veil Nebula, where the C1's OIII band picks up the blue-green filaments.
• Sulfur-rich regions for the C2: the Crescent Nebula, the Tadpoles in IC 410 and the Elephant's Trunk in IC 1396, where SII adds the warm gold tones of an SHO image.
• Planetary nebulae: the Ring, Dumbbell and Helix Nebulae in strong OIII.

The filters don't help with galaxies, star clusters or reflection nebulae, which shine in broad starlight. Use an unfiltered camera or a broadband filter for those.

How it works

A color camera records red, green and blue through a pattern of tiny filters on the sensor. With the C1 in front, the red pixels record hydrogen-alpha and the green and blue pixels record oxygen. With the C2, the red pixels record sulfur and the green and blue pixels again record oxygen.

1. Shoot a set of exposures of your target through the C1, then a set through the C2. Many imagers spend one night on each.
2. Stack each set separately. Split the C1 stack into its Hα (red) and OIII (green and blue) data, and take the SII (red) data from the C2 stack. The OIII from both nights can be combined for a cleaner result.
3. Map SII to red, Hα to green and OIII to blue for the classic Hubble palette, or try other blends. Software such as PixInsight, Siril or Astro Pixel Processor can do the channel extraction.

The C1 on its own also makes good-looking two-color (HOO) images, so many people start with it and add the C2 later.

Fits / works with

• Askar telescopes with a 2" filter thread in the camera adapter: the 50P, FMA180 Pro, SQA55, SQA60 Pro, SQA70, 60F, 71F, 91F, 111F and 131F.
• Filter drawers, which make swapping between C1 and C2 easy without disturbing focus or framing: the ZWO M42 2" filter drawer or M54 2" filter drawer, with an extra 2" filter holder so each filter has its own. Good for the SQA85, SQA106 and SQA130.
• Color astronomy cameras such as the ZWO ASI2600MC Pro, ASI2600MC Air or ASI533MC Pro.

The 2mm glass moves the focus point back by about 0.7mm, so refocus after adding a filter, and allow for it if your telescope needs exact camera spacing.

C package vs. C1 or C2 alone

Askar also makes the narrower Colour Magic D series (6.5nm OIII, 8.5nm Hα or SII) for darker backgrounds under a bright Moon. See all Askar telescopes and accessories.

What's in the box

• Askar Colour Magic C1 2" duo-band filter (Hα + OIII)
• Askar Colour Magic C2 2" duo-band filter (SII + OIII)

The camera, filter drawer and telescope are sold separately.

Colour Magic C package FAQ

Do these work with a mono camera?

They're designed for color cameras. With a mono camera, each filter records both of its emission lines mixed together, so separate single-line Hα, OIII and SII filters are the better choice.

Are they good for beginners?

The C1 is a good first narrowband filter for a color camera. The full SHO workflow with both filters is better once you're comfortable stacking and processing.

Can I use them on a fast telescope?

Yes. Their wider bands are more forgiving of the steep light cone of f/2 to f/4 telescopes than 3–7nm filters, which can lose signal at fast focal ratios.

Do they fit 1.25" accessories?

No. These are 2" mounted filters. They thread into a 2" filter thread or sit in a 2" filter drawer.

C filters or a single duo-band filter?

If you only want two-color nebula images, the C1 alone, or a filter such as the ZWO Duo-Band or Optolong L-eXtreme, is enough. The package is for adding sulfur and making full Hubble-palette images.

Specifications