Review: Askar Colour Magic D1 and D2 Duo Band filters (Ha/OIII & SII/OIII)

Dualband filters have opened the world of convenient narrowband imaging to One-Shot Colour (OSC) camera users. Askar are hoping to shake things up further with the release of their Colour Magic D1 and D2 filters which, when used in combination, allow for full SHO imaging.

SHO imaging for OSC users

Narrowband imaging used to be the preserve of astrophotographers using mono cameras and three key filters: Hydrogen-alpha (Ha), Oxygen III (OIII), and Sulfur II (SII). However, a few years ago the introduction of dualband filters hugely increased the versatility of OSC cameras. These new filters, such as the Optolong L-eXtreme allowed OSC imagers to efficiently capture Ha and OIII wavelengths using just one filter. While not quite as effective as a mono camera plus three dedicated filters – SII, Ha, and OIII –the results using these dualband filters proved to be surprisingly effective, while being much cheaper. I’ve used an L-eXtreme extensively – click here for lots of examples, and check out my article on OSC vs Mono from a City. There was always a catch, however: the lack of SII data. Dualband imagers had to decide whether to create bi-color images, or use software solutions to create a pseduo-SII channel.  

Enter Askar, who have just released a new set of 6nm dualband filters aimed at OSC imagers, currently available 2″ mounted. The first of these, called the D1, is fairly standard, capturing Ha and OIII data. The D2 is what could be a game-changer, capturing SII and OIII. By combining data from these two filters, Askar claim that the results are very similar to using a mono camera and full set of filters.

Processing

Being an OSC imager myself, I was very excited to put these filters through their paces. I already had eight hours of Askar Colour Magic D1 data on the Elephant’s Trunk Nebula taken for my dualband filter shootout article. I took another eight hours using the D2 filter, all with my lovely new Askar 130PHQ refractor (review here).

After integrating the two stacks in PixInsight and applying a quick autostretch, it was evident that the two filters were indeed collecting different wavelengths of light.

I then followed the first part of a short processing tutorial provided by the manufacturer. The basic steps are to integrate the data from each filter separately, and ensure that the two resulting images are aligned to one another.

The D1 integration is then renamed “HO” (i.e. Ha and OIII); while the D2 integration is renamed “SO” (i.e. SII and OIII). Each integration is then split into its constituent RGB channels, which are promptly renamed:

HO_R renamed to H
HO_G renamed to O1
HO_B renamed to O2

SO_R renamed to S
SO_G renamed to O3
SO_B renamed to O4

So, the red channel from the D1 filter is taken to be the H channel. The red channel from the D2 filter is taken to be the S channel. The four remaining channels – called O1, O2, O3, O4 – are integrated into one image, which is renamed O. Hey presto, we have SHO channels from two filters.

There are different ways of reaching this step, and what I’ve outlined is a simple approach just to convey the general idea. Once you have the SHO channels, you’re into the workflow of mono imagers.

Target one: The Elephant’s Trunk Nebula

There are as many different processing workflows as there are astrophotographers, so I simply aimed to produce a colourful image to bring out the data that these filters captured. I was pleased with the result, in particular with the blues that often prove elusive when processing regular Ha OIII dualband data.

There were some challenges, such as overly purple stars, that I did my best to deal with. Experienced mono imagers would no doubt take all this in their stride, but OSC imagers may need to learn a few new tricks. (I found PixInsight’s “CorrectMagentaStars” to be useful).

As mentioned earlier, regular Ha OIII dualband imagers have the option to create a pseudo-SII channel during processing. This is quite simple in PixInsight thanks to a one-click process described here. How would an Ha OIII image processed using this technique compare? Fortunately, using that technique as a foundation I had previously created an image from a 22-hour integration from my Bortle 8 city centre using purely Ha and OIII data (specifically, 11 hours from an Askar Colour Magic D1, and 11 hours from an Optolong L-Ultimate 3nm. Click here for a whole post about that image, or use the slider below to compare:

A quick straw poll among fellow astroimagers, as well as non-astro friends, revealed a split in opinion over which image is better. Personally, I prefer the pseudo-SII version, which may be because the image was slightly higher quality as a result of the cleaner 3nm Optolong L-Ultimate data.

Target two: The Heart Nebula

The Heart Nebula has plenty of OIII, so I decided it would make a good second target for my tests. I collected 12 hours of data using the Askar Colour Magic D1, and then another 12 hours using the D2.

I found this easier to process than The Elephant’s Trunk Nebula, perhaps due to the increased levels of OIII. I was very happy with the colour palette I managed to bring out, with the shades of blue in particular being something I’ve always associated with SHO mono images. The left part of the nebula is almost rainbow-like. I consider the result to be quite remarkable, especially considering this is from a city centre. Click here for a whole post about the image.

I then tried making an Ha OIII version with a pseudo-SII channel with data just from the Askar D1. The result is respectable but lacks clarity, likely due to the fact that it’s half the integration time. Try as I might though, I just couldn’t reproduce the glorious colours of the Askar D1 D2 combination. You can compare the two using the slider:

Post-test thoughts

It’s clear that Askar have produced something very impressive with their Colour Magic D1 and D2 filters. Study the Heart Nebula picture in particular and remind yourself that it was taken using an OSC camera!

Of course, it’s important to consider cost. The Askar Colour Magic D1 and D2 filters can be bought individually for £320 each, or as a pair for £620. Optolong have recently released their L-Ultimate Ha OIII dualband filter, which with a pricetag of £389 is more expensive than the individual Askars, but has 3nm bandpasses compared to the Askar D1 and D2’s 6nm. Check out my Dualband Filter Shootout for examples of how 3nm is superior to 6nm.

This presents OSC imagers with a dilemma: buy the Askar D1 and D2 filters, which allows for SHO imaging but at 6nm; or save £231 and opt for an Optolong L-Ultimate filter, be content with bi-color or pseudo-SII processing, but with the superior 3nm and the simplicity of using one filter instead of two. There’s not a clear-cut optimal answer, and it’s down to individual imagers to decide what’s the best route for them.

Note that Askar have their own 3nm Colour Magic Ha OIII filter (£595) that they’re sending me to review. Askar say they’re not currently planning on releasing a 3nm SII OIII filter. I think this is a shame, and it feels like Askar have come so close to causing a seismic shift for astroimagers. Imagine these D1 and D2 filters, but at 3nm and priced competitively. That would elevate them from impressive to truly incredible.

As it stands, the Askar D1 and D2 filters are still interesting propositions that could siphon imagers away from mono set-ups. If you’re a purist and want the absolute highest image quality, scientific accuracy, and flexibility, then mono still is – and likely always will be – the answer. But with filters like the Askar Colour Magic D1 and D2, you can choose OSC and get close for a much lower cost.

On a personal note, I’m going to keep experimenting with the D1 and D2. I want to do more tests pitting them against the L-Ultimate in particular. Once Askar send me their 3nm D1-equivalent filter to test, I’d like to try combining that with 6nm D2 data.

These Askar filters open up a lot of possibility, and I think that’s a brilliant thing in this hobby. Let’s have more imagers trying different things! I’d love to see a mono imager try these filters and see what the results are — there’s no law that says they’re exclusively for OSC cameras, after all.

Extra note, 11 Jan 2023

It’s been brought to my attention that some of these filters may perform better than others. See this Cloudy Nights forum thread, and this more general video from Cuiv about equipment lottery. I don’t have the required kit to test the reality of my filters against their specifications, but going by eye alone I think they’re OK. It’s worth bearing this “lottery” in mind if you do want to buy these filters though. First Light Optics have a robust returns policy, and if you’re buying second-hand it’s always a good idea to ask for example images.

Extra extra note, 11 Feb 2023

I’ve found that the Askar D2 filter combines very nicely with the Optolong L-Ultimate, which is like an enhanced version of the Askar D1. So, going forward for narrowband targets, if an object has a decent amount of SII in it, I’m going to collect data using my L-Ultimate and D2. If the target doesn’t have much SII, I’ll just use the L-Ultimate.

For example, this photo of The Soul Nebula combines Optolong L-Ultimate and Askar D2 data for SHO (and no filter for RGB stars).

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Nothing will motivate me to create more content quite like money!