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A first narrowband filter for color cameras that's easy to live with
Why we like the Colour Magic C1:
- Nebulae through city skyglow: it passes only hydrogen-alpha and oxygen light and blocks 200 to 1000nm at OD3 everywhere else, so emission nebulae stand out against a dark background even from the suburbs.
- Forgiving bandwidths: a 15nm Hα band and a 35nm OIII band pass more light than 3–7nm filters, so stars stay easy to focus and guide on, and the filter works well on fast telescopes such as the f/3.8 Askar 50P.
- Room to grow: add the C2 (SII + OIII) later and you have all three channels for Hubble-palette (SHO) images from a color camera.
- Worth knowing: the wider bands also let in more moonlight and skyglow than tight 3–7nm filters, so contrast drops under a bright Moon. It's made for emission nebulae; galaxies, star clusters and reflection nebulae are better shot without it.
The Askar Colour Magic C1 2" Duo-Band Filter (Hα + OIII) is a 2" mounted dual-band filter for one-shot color astronomy cameras. Your camera's red pixels record the deep red glow of hydrogen-alpha at 656.6nm, and its green and blue pixels record the blue-green glow of doubly ionized oxygen at 500.7nm, which makes it simple to produce natural-looking two-color (HOO) nebula images. It's the same filter as the C1 in the Colour Magic C package.
Key specs: Hα 656.6nm, 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 cell
What you can image
- Bright emission nebulae: the Orion Nebula, the Lagoon and Trifid Nebulae, the Eagle Nebula and the Rosette Nebula.
- Big, faint nebula fields: the Heart and Soul Nebulae, the North America and Pelican Nebulae, and the California Nebula.
- Oxygen-rich targets: the Veil Nebula's filaments and planetary nebulae such as the Ring, Dumbbell and Helix Nebulae.
How to use it
Thread the C1 into a 2" filter thread in front of your camera, or put it in a 2" filter drawer, and refocus: the 2mm glass moves focus back by about 0.7mm. Expose as usual, typically a few minutes per frame on a guided mount. In processing, the red channel holds the Hα data and the green and blue channels hold OIII. A simple HOO blend gives red hydrogen and teal oxygen, and many processing tools can stretch each channel separately for more color.
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: the ZWO M42 2" filter drawer or M54 2" filter drawer let you take the filter in and out without disturbing the camera; good for the SQA85, SQA106 and SQA130.
- Color astronomy cameras such as the ZWO ASI2600MC Pro, ASI2600MC Air or ASI533MC Pro.
C1 vs. C2 vs. the C package
| C1 (Hα + OIII) | C2 (SII + OIII) | C package (C1 + C2) | |
|---|---|---|---|
| Emission lines | Hα 656.6nm, OIII 500.7nm | SII 672nm, OIII 500.7nm | Hα, SII and OIII |
| Bandwidth (FWHM) | Hα 15nm, OIII 35nm | SII 15nm, OIII 35nm | Same as each filter |
| Images you can make | HOO bicolor | SOO bicolor; SII data for SHO | Full SHO Hubble palette, HOO, SOO |
| Best for | Your first narrowband filter for a color camera | Adding sulfur to an existing C1 | Going straight to Hubble-palette images |
Askar also makes the narrower Colour Magic D series (6.5nm OIII, 8.5nm Hα) 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)
The camera, filter drawer and telescope are sold separately.
Colour Magic C1 FAQ
Is the C1 good for beginners?
Yes, as a first narrowband filter for a color camera. Its wider bands are easier to focus and guide through than very narrow filters, and HOO images are simple to process.
C1 or ZWO Duo-Band?
Both pass Hα and OIII with similar band widths. The C1 pairs with Askar's C2 for Hubble-palette images; the ZWO Duo-Band also comes in a 1.25" size.
C1 or Optolong L-eXtreme?
The L-eXtreme has much narrower bands for more contrast in bright skies and moonlight. The C1 passes more light, which helps on fast telescopes and with guide cameras built into the main camera.
Does it work with a mono camera?
It's designed for color cameras. A mono camera records both lines mixed together, so single-line Hα and OIII filters are the better choice.
Specifications
| Optical | |
|---|---|
| Center wavelengths | 500.7nm (OIII) and 656.6nm (Hα) |
| Bandwidth (FWHM) | OIII 35nm ± 5nm; Hα 15nm ± 3nm |
| Peak transmission | 90% |
| Blocking | OD3 from 200 to 1000nm |
| Surface quality | 60/40 scratch-dig |
| Physical | |
| Glass thickness | 2mm ± 0.05mm |
| Size | 2" mounted |
| Model / SKU | Askar Colour Magic C1 Duo-band Filter (Hα+OIII) / CM-C1 |