Kevin_A Maybe you can test out 150, Unity and HCG and see what your thoughts are.

I just measured two sets of dark frames at -10ºC. One set is at Unity gain, and the second set is at HCG gain.

When I compare the HCG (at half the exposure time of the Unity gain, to equalize the exposure value) with Unity gain, the HCG definitely has lower standard deviation (a.k.a. RMS). Not by much, but definitely there.

The dark current noise is still very dominant -- i.e., you can see the noise rise with exposure time (read noise should be constant with exposure time -- one read per exposure).

This is just one noisy camera for long exposures.

From that result, I think I will try HCG tonight with 100 sec exposure. Also abandon the Antlia RGB and use the Baader Neodymium instead. Moon is going to be nasty -- with more than 60% illuminated (the neodymium might help a little).

The HCG gain also has slightly better dynamic range than gain 150.

I'm taking some -10ºC dark frames at gain 252 and exposure 100 seconds right now to prepare for tonight. I still don't have dark and bias for last night's Unity gain and 180 sec. So, can't process those yet.

Right now, I am not sure it is worth getting the smaller pixels vs using the ASI2600. I can always teleextend the FSQ-85 by 1.5x for the larger 2600 pixels -- slows it down to an f/8 though. I think the 585 is just a cheap cooled camera - better than nothing, but not competitive with the better sensors.

BTW, does it irritate you that the long edge of the sensor, relative to the USB connectors, is 90 degrees from the ASI2600 orientation. No adult supervision.

Chen

Kevin_A I think if I remember even 60s at HGC the hot pixels were plenty!

Yuk. Too noisy (albeit there is no bias, darks or flats here, just simple stacking):

This is what I got in 2022 with the ASI2600MM with just 50 subframes (180s HCG):

I think I give up on the ASI585 and try the color ASI2600MC tonight :-).

Chen

Kevin_A it is limited in its use

From my dark frame tests, it is perhaps a "short-exposure-time" camera. Perhaps the cooler can keep the sensor cooled while taking EAA frames? (I don't do EAA, so it is not useful for me.)

Won't work with dim targets that are below sky backgrond noise for my Bortle 5-6 either. (I don't have your dark skies :-) Just chalk another one up as a lesson learned. So far, my favorite ZWO cameras are the ASI071 (now way obsolete), and both the ASI2600 (color and mono), and of course the ASI178mm for guiding (consistently giving me better than 0.4" total RMS with gain of 27 dB). The 294 has many quirks, so I just use a discarded one as my All-Sky camera.

Chen

Kevin_A I am going to shoot my next session at HGC and use 90s exposures

Yeah. Keep the exposure duration low.

Heck, I can try that tonight. I might try 100 seconds HCG, since I already made dark frames for it. The exposure value should be very close to 180 seconds at Unity gain.

Chen

Kevin_A 12 bits not to get oversaturation?

12 bits is 4*1024 = 4096 :-).

Didn't I suggest earlier that DSO'ers who can afford it already have bought the IMX571 cameras? This one is for people who can't afford them, but want a cooled camera. To get the same dark current noise, you need to use exposure times that is like 1/10 of the ASI2600. Not sure cooling it is worth the money.

I have one EFW what has 36mm Chroma LRGBSHO for the ASI2600MM (my all-time favorite camera so far); the 585 is just a curiosity piece. Also have 2" Chromas, but not as convenient since they are mounted on two separate 2" EFW. I also like just using a Luminance filter with the 2600MM; rminds me of the Tri-X days :-).

I tried 100 sec at HCG last night. Appears much cleaner, even though the skies were much worse than the night before. Will make some flat frames and flat darks later.

Next few days will be cloudy, so last night's capture will be the last for a while. Right now, I have another project in the works that I can work on when it is cloudy (fork mounting the guide scope so that it is on the counter-weight side of the RST-135 -- the FMA180p with EAF clocks in at 1.3 kg (10% of the rated 13.5 kg payload specs of then RST-135!), so this will move 1.3 kg from the declination clamp side of the RA axis over to the counterweight side.

Chen

Kevin_A Even at max cooling the dark current noise is still only equivalent to a 2600 at 0c.

Unfortunately, many ZWO customers don't even look at that dark current curve. Those who buy this camera as their primary camera will eventually have to upgrade (and the total out-of-pocket to them is more, at the benefit of ZWO). I tend to pick the top of the line (and thus more expensive) devices -- that way, I save money on the long run, not having to constantly "upgrade."

I think that will be the most I can get out of this camera and cooling

Shame since your dark Bortle allows very long exposures before the sky background saturates.

I think the EAA folks will be quite happy with it, though. They can run at 30 seconds, and be mostly read-noise dominated.

For me too this is a novelty camera, but if any knowledge and useful data can help others get the most out of it I will have done my job.

Yeah, it is fun tinkering and learning for me too. But this one will probably end up in my pile of less-used cameras (unless I try one day to build a "smart telescope" based on Indigo).

Chen

Kevin_A For me too this is a novelty camera, but if any knowledge and useful data can help others get the most out of it I will have done my job.

Speaking of which, I will probably get the smaller Skywatcher Wave (10 kg) to see if they can be made to guide well with the small camera lenses. Even if I can't get 0.4" guiding, at least the short focal lengths can withstand 1" of error.

I just want to see how bad these non-RainbowAstro mounts are using what I know about autoguiding. The 10kg version of the mount mount is probably under $2K when it comes out; perhaps mid $1k even. (Note: company HQ in Taiwan, not China; so there is a chance that the QC is globs better-- probably not Japan or Korea quality, but better than what Chinese companies pass as QC.) Heck, 10 kg might even carry my FSQ-85: 6.4 kg with 7-filter 36mm EFW and ASI2600. Add my FMA180p at 1.3 kg for guiding, and I am under the engineering specs.

My favorite Seattle telescope store actually deals with Skywatcher; I may ask them to look out for when I can preorder.

Chen

Kevin_A do you feel that there is much advantage taking darks with the 2600 series along with flats and flat darks?

I do it because that is what the math says about sensor errors (albeit small for something like the 2600).

Now, if you are concered about the dark frames adding noise to the result, I don't think you need to be. If you make up the dark frame (basically, same exposure parameters as the light frame) with 1 single dark frame, you will be decreasing the SNR by 3 dB (i.e., you are adding the same amount of noise but no data -- the lens is capped). I.e., the total noise is sqrt( L² + D² ) where L is RMS of the Light frame and D is the RMS of the Master Dark frame. Since L=D (D is noise from a single Dark frame, remember?), we have total noise = sqrt(L² + L²) -- thus we are doubling the total noise after adding the Master Dark to the LIght, and thus a 3 dB increase in noise. This then translates to 3 dB worse signal to Noise ratio. Not so good -- but remember, the Master Dark is made of only 1 single Dark frame.

OK, once you grok the above, now consider making the Master Dark from 2 independent dark frame (again, just two frames), The Master Dark now has a noise that is 3 dB less than the noise from the 1-frame Master Dark. So, now you are adding 3 dB less noise to your LIght frame. The total noise from the 2-frame Master Dark and the Light Frame is now sqrt( L² + (L²)/2 ) = L*sqrt(1.5). Ha ha, noise power (variance), the inside of the sqrt, has gone up by just 1.5 now (not 2).

log10( 1.5 ) = 0.176, and thus 10.log10( 1.5 ) = 1.76 dB. Yippee, the noise has ony increased by 1.76 dB now, by using 2 Dark Frames instead of 1 Dark Frame.

Now, if you double the number of Dark frames again, to 4, the second argument in the sqrt halves again. So, a Master Dark with 4 Dark Frames will create a total noise of L*sqrt( 1.25 ) or 0.96 dB. Your final SNR is now worse only by less than 1 dB now.

OK, lets take 16 Dark frames. The sqrt is now sqrt( 1.0625 ) or 0.263 dB worse.

With 32 dark frames, the SNR worsens by only 0.133 dB. With 64 dark frames, the SNR worsens by 0.0673 dB.

I doubt very much that the human eye could tell the difference of 0.1 dB in SNR. So with just 50 dark frames, you can be pretty sure that applying the Master Dark would not ruin your final image.

I usually do between 20 and 30 cal frames of darks, flats and flat darks to create masters.

I still would recommend more than 20 (0.21 dB SNR degradation), though, since how often do you take Dark frames for the library anyway. So you can knock yourself out, and take 100 dark frames (I use between 100 and 200, but I am an OCD engineer :-) and there is no way Superman can telll the difference. At the same time, the ASI2600 dark current noise is likely to be more than +0.1 dB, in which case applying a Master Dark will improve the final SNR, not worsen it.

Once you create a Master Dark, the actualy processing time in the future is a constant, whether the Master darkk started with 10 Dark frames or 1000 Dark frames.

Whether it is worth it is up to you, but I typically start up AstroPixelProcessor and walk away. Plus, my Mac Studio Ultra has 128 GB of RAM and I give 96 GB to AstroPixelProcessor -- not typo - 128 Gigabytes of RAM; I maxed out the memory that the Studio can support when I bought it, since the plan is to use the computer for 5 years -- it has been 2 years already. I give AstroPixelProcessor all 20 cores of the CPU. So, I have no idea how much extra time it takes with or without applying Dark frames, but we are probably talking seconds extra. (The extra money spent on maxing out the Mac Studio has probably paid for itself in time saved, already, without having to upgrade the computer every year -- just like extra money spent on Takahashis :-).

Chen