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The sulfur channel your color camera has been missing
Why we like the Colour Magic C2:
- Completes the Hubble palette: most dual-band filters for color cameras capture only Hα and OIII. The C2 records sulfur (SII) and oxygen, so with a C1 you have all three channels for an SHO image without a mono camera and filter wheel.
- Forgiving bandwidths: a 15nm SII band and a 35nm OIII band pass more light than 3–7nm filters, which helps with faint sulfur signal and with fast telescopes.
- Dark backgrounds: outside its two bands it blocks 200 to 1000nm at OD3, so skyglow drops away and the nebula stands out.
- Worth knowing: sulfur is the faintest of the three nebula lines, so plan on more exposure time than with the C1, and expect to blend it with C1 data in processing. The wider bands also let in more moonlight than tight 3–7nm filters.
The Askar Colour Magic C2 2" Duo-Band Filter (SII + OIII) is a 2" mounted dual-band filter for one-shot color astronomy cameras. Your camera's red pixels record ionized sulfur at 672nm and its green and blue pixels record oxygen at 500.7nm. On its own it makes striking two-color (SOO) images; combined with the C1's hydrogen-alpha data, it gives you the classic Hubble palette. If you need both filters, the Colour Magic C package costs less than buying them separately.
Key specs: 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 cell
What you can image
- Classic SHO targets: the Eagle Nebula and its Pillars, the Soul and Heart Nebulae, the Lagoon Nebula and the Rosette Nebula.
- Sulfur-rich regions: the Crescent Nebula, the Tadpoles in IC 410 and the Elephant's Trunk in IC 1396.
- Oxygen detail: the Veil Nebula and bright planetary nebulae, where the OIII band does most of the work.
How to make an SHO image with the C1 and C2
- Shoot a set of exposures through the C1 and a set through the C2, on the same framing. Refocus after each swap; the 2mm glass moves focus back by about 0.7mm.
- Stack each set separately. Take Hα from the red channel of the C1 stack, SII from the red channel of the C2 stack, and OIII from the green and blue channels of either or both.
- Map SII to red, Hα to green and OIII to blue for the Hubble palette, using software such as PixInsight, Siril or Astro Pixel Processor.
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 for quick swaps between C1 and C2: the ZWO M42 2" filter drawer or M54 2" filter drawer, with an extra 2" filter holder; good for the SQA85, SQA106 and SQA130.
- Color astronomy cameras such as the ZWO ASI2600MC Pro, ASI2600MC Air or ASI533MC Pro.
C2 vs. C1 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 |
See all Askar telescopes and accessories.
What's in the box
- Askar Colour Magic C2 2" duo-band filter (SII + OIII)
The camera, filter drawer and telescope are sold separately.
Colour Magic C2 FAQ
Do I need the C1 too?
For a full Hubble-palette image, yes: the C2 supplies sulfur and oxygen, and the C1 supplies hydrogen-alpha. The C2 alone makes two-color SOO images.
Is the C2 good for beginners?
We'd start with the C1, which captures the brightest nebula light and is simpler to process. Add the C2 once you're comfortable stacking and combining channels.
Does it work with a mono camera?
It's designed for color cameras. A mono camera records both lines mixed together, so single-line SII and OIII filters are the better choice.
Can I use it on a fast telescope?
Yes. Its wider bands are more forgiving of fast f/2 to f/4 light cones than 3–7nm filters.
Specifications
| Optical | |
|---|---|
| Center wavelengths | 500.7nm (OIII) and 672nm (SII) |
| Bandwidth (FWHM) | OIII 35nm ± 5nm; SII 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 C2 Duo-band Filter (SII+OIII) / CM-C2 |