What was your experience switching from ASI2600MC to ASI2600MM with exactly the same scope?

I would love to see that as well. It seems on paper that the resolution and S/N difference should really be apparent but in the tests I've seen, it doesn't seem to be. I believe Cuiv did a YouTube video doing exactly such a comparison.

Hi,

I don't own neither the ASI2600MC nor the ASI2600MM, but I switched from the ZWO ASI533MC Pro to the Player One Ares-M, two cameras that use respectively the color and mono versions of the IMX533 sensor (basically the same sensor as the IMX571, just smaller).

With this upgrade I also added an 8 position filter wheel and an electronic focuser. My telescope (or to be precise my lens) is the Samyang 135mm f/2.0.

I can tell you that the difference in terms of SNR using narrowband filters is night and day, of course in favor of the mono camera. The difference is a bit smaller with broadband filters and LRGB, but it's still there.

I also found that adding a filter wheel and a focuser (I set up filter offset to focus once with luminance and not with every filter) helped everything being more automated. I can change filters without waking up and unscrewing the imaging train and I can also set up a sequence to shoot a broadband target until the moon rises and then switch to a narrowband target.

IMO it makes imaging different and more impactful especially when the narrowband single subs are rolling in. I could achieve similar (a little lower, but still very high) SNR levels with the H-alpha filter and mono on NGC 1499 with 45 minutes of exposure, to the red channel of 20 hours of exposure with the L-eNhance and OSC.

The only thing a bit more difficult is shooting flats for every used filter for each session instead of just one set of flats (and also managing all the different files).

This was my first light of the mono camera on NGC 1499:
​​​

And this is a different work I did last year with the ASI533MC Pro:


If you have the budget and you can stand the work of multiple filters, you'll be very satisfied.

Daniele

andrea tasselli:
If I were to chose between the two shots I'd chose the second one (IMX533C) without even a second glance.

What I tried to point out is that with such a short integration, a little bit over 2 hours, the first shot (IMX533M) is close (what I mean with close is that the emission part of the nebula has a similar SNR) to the second shot (IMX533C), with 21 hours of integration with the L-eNhance.

I would contend that a 12nm passband filter is no match to a 6 nm passband filter.

Cuiv's video on the subject may shed some light:

https://www.youtube.com/watch?v=CooWNVq6rj8&t=1016s

Not the perfect comparison but interesting.

There's no doubt about the efficiency but for for me, it would be a very large cash outlay to go from OSC shooting dual band as I do now, to a complete mono setup. I believe the 533 is the least expensive camera at $900.00, add the filter wheel $260.00, filters will run at least $630.00 or a lot more and lastly an EAF $200.00. That's about $2000.00 at a minimum. To be fair, the EAF and the filter wheel would have some utility in OSC but I also start thinking about some very nice OTA's I could buy with that same amount of cash. For me at least, it's a hard sell.

This makes me very anxious to get rid of the CFA on my 2400.

I have no deepsky experience with the 2600mono version, but have used the 2600MC for NB for years now, and am really happy with it. I did make a deliberate decision to go with OSC, but did my research first. So there are a few points I can make based on my experience, and a lot of reading.

Simplicity and cost was a factor–I hate doing flats and they can go wrong in so many ways. The thought of doing flats for LRGBHaOIIISII gave me pause. Also 7 filters! I now use three, an SO and an HO filter with my OSC, plus a LP pollution for WB. But note to get here, I went from the L-eNhance, to L-eXtreme, to L-Ultimate for HO as the technology got better in the filters. For SO and LP I also upgraded, so have with upgrades bought 7 filters. If you have 7 filters to begin with that you want to upgrade, you may need deeper pockets. And of course you need an automated filter wheel with mono. 

My sky conditions, especially seeing change dramatically over a night. With mono, you have to worry if the seeing was worse with one color than another you will get halos, so you need to correct somehow for that. For things like comets that are moving, mono would be more painful. And for planets, an OSC is so much easier since the planets are rotating and seeing conditions are so important. 

As to signal comparison.

Say you have a patch of Ha in the sky. For mono NB you get 4 pixels of Ha, compared to 1 pixel for the OSC. So for Ha, OSC will need about 4X longer exposure to the same S/N. But note, at the same time you are capturing 3 pixels of OIII with the OSC, but you are getting no pixels of OIII in mono. So if there is OIII there in that patch as well, then to capture that with mono you would need to half your time on Ha, then switch to OIII for the other 1/2 fof the time (or whatever fraction you want). Of course you would want to do this anyway, unless you are just making a red Ha image, as you want to color balance to get a full color image presumably. This halves your mono Ha advantage to 2X since we will use 1/2 the time for that, and 1/2 the time for OIII, so 1/2 time x 4/3 pixels= 4/6 the OIII signal compared to the OSC. This means you would need to spend 1.5x more time on the OIII with the mono camera. So the mono camera has a 2X Ha advantage and a 1.5x disadvantage in OIII. There is a difference, but it is not huge.

Personally I find many nebula are super strong in Ha, but relatively weak in OIII. So I can tolerate the fewer pixels of Ha to make my signal, and take advantage of the strong OIII signal I get at the same time. Of course, with mono you can choose to shorten your Ha and lengthen your OIII to adjust, which you cannot do with an OSC camera. Still, if you are interested in OIII, OSC is not far from mono, if you are interested only in a mono Ha image, mono is a clear winner.

Now, using NB filters with Bayer filters does loose some signal, maybe 20%, compared to mono. On the other hand, debayering averages pixels, so it improves S/N, kind of a partial binning if you like. So these two factors are probably close to a wash.

Note Blair McDonald has a great article in JRASC (the Journal of the Royal Astronomical Society of Canada), April 2022, P79. You may be able to find a copy in a local university library, I can't share it obvious due to copyright. It used the 2600MC and MM in RGB imaging, and found that in that case, generally there is slight advantage to OSC over mono. It does again depend on the target. He does all the math as well, it is a very well done article.

Regarding resolution, you must take into account your particular setup, focal length and pixel size, as well as seeing.

If you are totally limited by seeing and not by your pixel scale, then obviously no way a mono camera can do better in resolution than an OSC camera, it is the seeing the decides what you resolve. Case closed. In my own case, my deepsky work is always seeing limited, since I am at long FL (1430 mm), this is to be expected.

If your pixel size is determining your resolution, the resolution is not as bad as one might naively think with an OSC. First, the debayer actually can recover some detail, there are lots of scientific papers on debayering and finding better algorithms, since it is critical to consumer cameras. There is even a debayer drizzle. Further, every frame you take is slightly offset from the last one, even with the best guiding. This helps fill in the gaps. All one needs is a shift of 1 pixel to fill in the gaps. If you dither this will do it as well. 

I do planetary imaging with an OSC and am very happy with the resolution I get there, again my seeing, even with lucky imaging, is my biggest limitation.

Finally, I have been in this astrophotography journey for about 8 years now. My plan has always been to start simple stupid, and then work my way up if I saw the need. My experience is for spending money, at least if you want to do long FL imaging, is to get the best mount you can possibly afford, then see what you have left.

I hope this helps.
Rick

Frédéric Ruciak:
Hi Rick,
thank you very much for your comments. I found a free access to your article here and the reading is truly interesting as it is going beyond tradtional analysis. I recommend it.
CS Frédéric

That's interesting, I had though one had to be a member, like I am, to access it. It is a very good article, but am waiting for his follow up with NB...Great you were able to read it.

Frédéric Ruciak:
Yes, but I guess the rationale is playing even more in favour or Mono camera this time. CS Frédéric

Yes, certainly for Ha only. For a mixture of Ha/OIII in a target it will be reasonably close I think, though it will obviously be better in mono to some extent, and again in mono one can tailor the exposure times in Ha and OIII depending on their relative strengths in the target, to do even better. I thought I had seen a good video that did the analysis of mono and OSC in a systematic way for NB, but I can't find it right now. Most videos seem to be just "my" opinion pieces, without any systematic data to back them up.

I've been imaging with a Poseidon-C (same sensor as the 2600),  Askar FRA600 with L-ultimate and Askar D2 filters for about 10 months and just got a Poseidon-M, filter wheel and Antlia 3nm SHO and pro series LRGB last month.   I don't have any data that you could compare apples to apples, but since I got the mono setup, I haven't used the OSC.  IMO the data for narrowband is cleaner and the images are sharper, but I feel OSC could close the gap with a lot longer integration.  For Broadband, I don't feel there is a whole lot of difference. 
The automation in Nina has made setup easier with the Mono vs OSC.  Using the L filter for plate solving, autofocus, and polar alignment speeds things up a lot.  The versatility with mono is another plus being able to shoot whatever band you want.  I've only had mono for a month now so the fun factor may wear off some, but I would go to Mono again in a heartbeat.

Rick Veregin:
1) Regarding the effect of debayer, this is from the scientific papers around bebayer, not my opinion. It is very much like a binning process, though not as harsh on resolution as 2x2 bin, but certainly with mono you can do a bin to gain an advantage, but one could do the same for the OSC and get almost the same benefit. Unless you are saying binning a CCD camera, that is a different kettle of fish. Anyway, the OP is interested in the same CMOS camera, mono vs OSC, so CCD is a different topic.

I should be more clear with what I am saying here. The 2600MM camera, as a specific example of (say) H-alpha, will capture 26 MPix of data, each pixel of which is independent from a noise standpoint with respect to its neighboring pixels.

The 2600MC will capture only 6.5 MPix of noise independent pixels, the rest reconstructed through debayering. These are not independent from a noise standpoint, and that is a key factor.

Now, if debayering was the solution to SNR (as opposed to resolution), think about what I could do with the 2600MM frame. 

I could split that into four 6.5 MPix frames, each noise independent of the other (since the photons incident are both spatially and temporally random), debayer each of those, and essentially get four times the signal of the 2600MC in the same time.

This has nothing to do with CCD versus CMOS, but is inherent in the basic statistics of photon capture that are independent of the recording method. Think about it - if it was truly possibly to get the same signal to noise by splitting your subs and debayering them, why stop at four? Why not eight or sixteen?