Spongey

That makes sense, of course. I was more referring to those sensors we typically use in astronomy (that would generally have <40% QE between 400-700nm). I think I understand your other point. My question, I suppose, is that given a particular optical train, e.g. Baader RGB filters and ZWO AR window, how will changing the sensor behind it (e.g. mono ASI1600 vs. mono ASI2600) affect the resulting colour gamut, if at all?

Great posts Vlaiv! I have a question: how much (if at all) does the QE response of the camera affect the resultant gamut output? I would assume none, as a different scaling transform could simply be applied based on the response of the sensor, and this would only affect the brightness of the colours, not their gamut. I appreciate the AR window on the camera affects the response, so is the resultant gamut output only a function of the filters used and the AR window?

Thanks! I'm bortle 4/5, with the worst pollution in the west, so sticking to targets as they rise tends to work best. Unfortunately that limits me to ~3-4 hours per night, as soon after the meridian the sub quality gets noticeably worse. I typically find that ~3 hours is a minimum to get reasonable data, much less than that and things become very noisy.

I managed to get another 3 hours of useable data on Tuesday night before the clouds rolled in. Tried to bring out some more contrast between the background and the fainter dust in this process, thanks to the improved integration time. This may end up being my last image with my 6D for now, as I've placed an order for a QHY 268M! Cheers

The 268M does ship with a bolt on M54 to M48 adapter as shown below. This could be bolted to the front of the camera instead, but would take up an additional 5mm backfocus. Not sure if that helps you at all.

The camera does not appear to have any dovetail adapter, as is present in the colour version. No photos I've seen of the camera seem to imply that there is. The camera can be bolted directly to the filter wheel, as seen in some of the above linked connection diagrams, similarly to the QHY600. With the QHYCFW3M-US (17.5mm thick), this gives a sensor to filter distance of 21.25mm, assuming the filter is centred in the filter wheel.

The backfocus of the 268M is 12.5mm. There is only one version (source). There is an attached drawing on the astrograph page that only refers to the 600M and 17.5mm, if that is what is confusing you? More info on adapters can be found on this page.

Considering that my main goal with imaging, ultimately, is to make pretty pictures, I have decided to go with the Baaders. Their reputation within the community, together with the SNR gain caused by the extended gaps present in the Antlia bandpasses were the deciding factors for me. While the colour of my photos might not be exactly as one would see them with the naked eye, I'm sure they will be good enough for me

I feel like this is a good question to pose to more experienced imagers than I, and perhaps even to filter manufacturers. A quick search doesn't return many results for photos made with the Astronomik type 2c filters. In fact, the only photos I can find are made with the Astronomik Deep-Sky RGB filters which have steep cutoffs.

For a scope like the RASA, where filter changes are inconvenient and having a wheel would increase the central obstruction, I think having an OSC makes sense. Of course, a mono camera with filters would produce better results, but you have already shown how capable the 2600MC is on a RASA, and I think that is more than enough for most folk.

This is fantastic news, and considerably under what I was initially expecting. Are you still looking to buy one Adam or are you sticking with the 2600MC? Cheers

While this is true and will be the best way to achieve true colour, I assume that the sharp cut on/offs of typical RGB filters are used to maximise signal, whilst producing colour that is 'good enough'.

This is true in the standard configuration, but the adjuster plate can be removed, as with the 2600MC and 6200MM/MC, in order to gain 5mm of backfocus. This then requires bolting the camera face onto the filterwheel, which is currently only possible with the 2" ZWO wheel, but there is supposedly a plan to release a bolted 36mm version too. It is worth noting that the existing QHY filter wheel works this way.

One thing that will make a significant difference to the minimum recommended filter size is the distance from the chip to the filter. Make sure you account for any additional distance introduced with the new camera (12.5mm backfocus minimum). With a 10mm filter wheel distance this would equate to 22.5mm sensor to filter distance, giving a minimum recommended filter size of 31.63mm and 31.33mm for 0.73x and 0.8x reducers respectively. The ZWO 1.25" filters appear to only have 26mm clear aperture (source), so you would experience significant mechanical vignetting with 1.25" filters with the 2600MM. 31mm unmounted filters would definitely help but 36mm are really the minimum for this camera with medium-fast optics.

Depending on your optical configuration you may need to upgrade to 36mm or 2inch filters. You can check the minimum recommended filter size for your optics and imaging train in this calculator.

Official price announcement. $2480 or pre-order until the end of Feb for $2280. No indication of how this translates to £. QHY have also announced that their first batch of 268M is available.

This is a very good point and I would not be surprised if the outcome of such an experiment is that the difference is small / inperceptable. Back to the topic at hand, another consideration for filter selection is filter bandpass and subsequent SNR. The SNR (assuming equal exposure lengths and everything else) of a sub in the blue channel for Baader and Antlia filters as shown above will be different, with the Baader filters having a higher value due to letting more light through. The same will be true for each of the colour channels actually, the Antlia filters have thinner bandpasses across the board. While I appreciate that these are to account for blue bloating and light pollution respectively, I think I would prefer the higher SNR provided by the Baader filters, as these still have a notch for spectral light pollution, and I would like to think that my optics are well corrected down to 400nm (I have no issues with blue bloat when using my Canon 6D with any of the above optics). With the way that light pollution is going, I doubt a wider gap here will retain its value. Cheers

Hi Vlaiv, Thanks for your response. This is of interest to me as I've recently been reading up on colour and its application in astrophotography. The cones in the human eye have spectral sensitivities that overlap (and even have negative responses), somewhat similarly to those in an OSC camera. Therefore, the only way to capture 'true' colour from deep sky objects would be to take images through spectral filters all across the visible spectrum, and subsequently apply colour matching functions to them to approximate the relative response of the human eye. If my understanding is correct, this is similar to how a chromaticity diagram is computed for all points not on the spectral locus. In practical means this is infeasible, and so how to best produce colour with three filters comes into question. I therefore logically come to the same conclusion as you; that filters such as the Astronomik LRGB type 2-c, or those used in OSC cameras are superior for creating true-colour images of deep sky objects. For true colour (or as close as practically possible) using these filters with a mono camera, colour calibration would need to be performed based on the filter response curves, sensor QE etc. As far as I'm aware, this isn't commonly done. My question therefore becomes why are these the only filters in a sea of LRGB filters to be designed in this way? Why is no one seemingly concerned with this issue? I don't doubt that good colour can be produced from filters with steep cutoffs such as Baader, Chroma, Astrodon etc., but if we astrophotographers were truly worried about producing true colour images then shouldn't we all be using ones similar to the Astronomiks? Cheers

Hi Martin, Thanks for your response! I will be using a 7 position filter wheel so no room for a clear filter I'm afraid. Furthermore, with my refractive optics, IR light won't be focussed to the same point as the visible spectrum so I'm not sure how useful a clear filter would be (probably less of an issue for EEVA). Cheers

Hi all, I am more seriously looking at filters now that the QHY268M / ASI 2600MM have been officially announced and are imminent. I have narrowband decided (Antlia 3nm PRO), but am still debating LRGB. I will be going with 36mm unmounted format. My main considerations are as follows: Imaging scope - Esprit 100, but I will occasionally use the camera with some canon lenses too; These lenses will be the Samyang 135mm (already owned), and potentially a Sigma Art 40mm should I delve into super widefield imaging at some point. Imaging location - My backyard is bortle 4/5, with a mixture of Hg/Na and LED based light pollution (mainly in the west). I will also travel (once we are allowed to) to dark sites a few times a year for holidays; Budget - I am looking around the £300 price point (i.e. anything except Astrodon and Chroma); Parfocality - This is between the filters themselves and my narrowband filters; and Backfocus - My narrowband filters will be 2mm thick, so ideally the LRGB will be the same to avoid any spacing issues. There are obviously a lot of options to choose from, such as Antlia, Baader, Astronomik, ZWO, Optolong to name a few. The current toss-up is between Antlia and Baader, but I am happy to be convinced otherwise. These filters are very similar in spec (2mm thickness, price), but their passbands are fairly different. I have copied each of the filter response curves below for convenience. My main concern with choosing the Antlia filters is the gaps in the spectrum around 400-420nm and 575-625nm. These are reasoned to combat blue bloat and light pollution respectively, but I can't help but feel that this a significant portion of the spectrum is lost, even if no major emission lines are in these bands. Is this likely to significantly affect colour balance / reproduction? The Lum filter looks good here. The Baader filters are established, have a small(er) gap for Hg/Na, but have a much earlier cut-up in the blue filter at around 380nm, which is also not included in the Lum filter. I doubt this would make a significant difference, but I am mildly concerned about blue bloat in my optics (mainly the canon lenses). The Lum filter also looks to have a slightly poorer response in the blue channel overall, and a significant peak around the 360nm point. Can anyone offer any advice / musings on any of the above? I realise I am likely to be happy with any of the listed offerings but lockdown is getting to me and this is how I am keeping my brain active! Baader: Antlia:

Not sure if this was resolved for you but I've been reading this thread on CN and it might be of interest to you. The whole thread is worth reading for background info but in particular posts #276 and #278 detail the problem you're having and the potential cause (in short, this is not caused by the filters and is instead due to centrally obstructed optics producing an extended airy disk which is being detected by the camera).

No problem This is the one piece of info that is yet to be official! Even if they are £50-100 more expensive then they will still represent great value vs. Astrodon and Chroma, especially considering their recent price hikes (providing they perform up to spec, of course).

I've been in touch with Antlia directly about these filters as they'd be the perfect match for the upcoming 2600MM / 268M (which I plan to buy). As you've noted all three filters will be OD5 rated (same as Chroma, Astrodon are OD4/5 I believe). 365Astronomy are the UK vendor for Antlia and I've been told by Antlia and 365 themselves that these will be in stock at the end of December. I'll be making an order for 36mm unmounted SHO filters when they are available! Just need the camera to come out too so I can use them! Cheers

Congratulations to the winners! Simply fantastic data and I can't wait for the next release

No problem, looking forward to seeing the result!