Mono Camera or Colour Camera?
There is a big choice to be made during your astrophotography journey: colour camera or mono camera?
A colour camera uses a sensor with a bayer matrix over it. Light passes through tiny coloured filters and is then read by the sensor. A mono camera has no such filter – the light is read as gray scale. In order to use a mono camera to construct a colour image we have to add filters in front of the sensor ourselves.
Recently I sold my Altair Astro Hypercam 183c colour camera to buy the mono version. Then I bought a filter wheel and a full set of narrowband filters. Since I particularly like the look of narrowband, and whilst it’s possible with a colour camera, a mono camera is more suited to narrowband imaging. I enjoyed the 183 sensor so much that when I saw the mono for sale – I took the plunge.
My Initial Mono Feelings
You may know that I live in the famously rainy and cloudy country of England in the United Kingdom. Most British dislike this because they dislike the clouds – and it’s of particular grievance when trying to photograph space. As such, it’s highly regarded that the weather in the UK isn’t suitable for mono imaging.
“It takes more time to complete an image”. – As we break down each channel separately it makes sense that it requires more time to make a picture. I feel this is the case – especially with narrowband imaging. With a one-shot colour (OSC) I would just point it at my target with a light pollution filter and image. When the Moon phase was up I would then use a Hydrogen-Alpha filter.
“It’s so much more work and effort to finish a picture”. – Again, down to using each channel separately the datam ust then be combined in post processing and the levels need tweaking and fiddling with to get a nice and natural looking image. An OSC sensor does this already and balances it out for a more natural look. With mono, it’s all in our hands and down to the editor to balance.
“It’s expensive”. – Yes. I can’t argue against this. For some reason mono cameras cost more – despite the fact it hasn’t got a bayer filter. I intend on asking manufacturers exactly why this is. Also then the cost of filters and a filter wheel. You got me there.
I was particularly resistant to the thought of going mono for these reasons. Though I would hear people argue that yes, you need to image channels separately and yes, it’s more work. But the data is much better. Better and cleaner data definitely appealed to me.
Again, it comes down to the bayer matrix. Instead of one red, two green and a blue pixel as with an OSC, all 4 pixels pick up blue, or red, or green etc depending on the filter. Ultimately I feel it’s a risk I took going to mono. But let me break it down further:
With a mono camera I need to be mindful about which Moon phase I’m in; I need to plan the night a bit more accordinly and add filter changes into my imaging sequence. That all sounds like a lot of work – but let’s think about this: Is it much different than what I did with an OSC?
With an OSC camera I would shoot narrowband (Ha) when the Moon was up. Making HaRGB composites became extremely enjoyable. Even from first quarter I would begin thinking of using the Ha filter. So has that big changed transitioning from OSC to Mono? Nope.
What about New Moon period? Well, with narrowband this is when I would go free range with my filters. But I would weigh most of the exposures to Oxygen-III (OIII). This is because Sulfur-II (SII) resists Moonlight a bit, and Ha all but blocks it out. So it’s easier to shoot SII and Ha when Luna shines bright – OIII struggles to resist Moonglow, so it makes sense to shoot OIII when the Moon isn’t out.
However I’ve been given a set of colour filters for my camera. So when New Moon approaches, I can pop them into my wheel and shoot colour. I, unfortunately, can’t find whether a light pollution filter is used with colour filters. So that is a test I shall perform in due course!
As for the swapping of filters, my imaging software takes care of that. All I need to do is make a plan earlier on and state how many sub exposures of what filter and how long. It then executes the plan and automatically swaps the filter when the time comes. Using carefully chosen parfocal filters (which means the focus doesn’t change between filters) I don’t need to worry too much about the channels.
I can, instead, be paranoid about PHD breaking randomly.
So how do I feel about my purchase and my prospects with mono imaging? I’m not an entire convert just yet. I still hold many reservations – I’ve only done two images so far from this mono camera. One of which was only Ha and OIII (Bi-Colour). However the data looks crisp and full of detail and I immediately saw a difference in the Ha sub exposures. I intend on shooting the Elephant’s Trunk Nebula again with the Skywatcher Evostar 80ED with the mono camera. So I can do a like-for-like comparison between the 183 mono and the 183 colour with a Ha filter.
What caught me off guard was the integration time. I didn’t realise how fast it can sneak up on you! As I was shooting through Moon glow, I kept with the Ha filter, and before I knew it I had broken 14 hours on one image between all three channels! So I’ll know for the future to diversify unless I’m doing a long project.
How do I feel about the actual challenge? I like the technical aspects and side of astrophotography. Working out the channel’s exposure lengths and blending them and figuring all that out is fun for me. So I’m excited.
Really though, in writing this article I think I may have convinced myself to like mono a bit more. When my night is, say, 3 hours – then I’ll make an image plan appropriate for it. If it’s one hour then I’ll mane a plan appropriate to that. However, if the night gets cut short by clouds and I haven’t got all the data – then I’ll miss OSC.
I’ll check in when I’ve more experience with this mono camera.