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Old 25-07-2020, 06:37 AM
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gregbradley
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I didn't realise til after this post your have the QHY183. I was writing about the ASI183. They seem to require different settings which is odd as they use the same sensor but that's the way it is.

Greg.



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Originally Posted by gregbradley View Post
I wrote a long reply and it didn't go through. Oh well here goes again.

I use gain 53 for broadband (LRGB) and Gain 111 for narrowband. Offset default at 8. Cooling to -10C or -25C.

I got these gain settings from John Rista's post on Cloudynights (a long thread about the 183mm) and from Lee on this site.

Exposure lengths are:

300 seconds for LRGB and 600 seconds for narrowband or for dim galaxies.

I also have tried 60 second exposure lengths for good colour RGB stars but yet to process images using that. Lee used 30 seconds for RGB stars in narrowband images and gets a great result.

I use 1x1 mostly but 2x2 for O111 and S11 and sometimes for RGB.

These cameras only use software binning so the gain is less than CCD.

111 is unity gain.

Amp glow dark subtracts out very cleanly so long as temperature, exposure length and gain are the same. Amp glow is also very weak on images with a bright object like M42 or M83. Even a 10 minute exposure of M83 shows hardly any amp glow. But a 10 minute exposure of NGC3521 shows a lot.

Don't use bias frames. Some use dark flats, I don't bother. These cameras are very clean and if not for the amp glow I would not bother with darks either.

These 2.4 micron small pixels behave a little differently to typical CCDs of 6-9 microns.

Firstly they are harder to focus. I find shifts in focus are smaller for the same change as on a CCD. It takes longer to focus.

The stars are rounder as more pixels are being used to display a star.

You can bin 2x2 and not lose hardly any resolution.

-10C should be achievable all year round as my camera on test cools to 47C below ambient.

-10C is very clean so deeper cooling has less than usual benefits. I am using -25C at the moment though as deeper cooling may also lower read noise and also reduces aritfacts. Not that the camera has any artifacts or lines etc. A very even and perfect sensor which makes sense as these sensors are from mirrorless and DSLR cameras.

Don't make it too complicated or it will become a mess of complication and difficult to process images.

Be careful with file naming, put the gain in the name of the file so you know what it was as CCDStack does not show what the gain used was.

I use The Sky X Pro and the ZWO Ascom X2 driver and it works very well, connects instantly and is very stable and robust. A big pus.

The camera is very light and small and outs no strain on the focuser or tracking.

The weakness of CMOS seems to be weak star colours. So watch that.

Also too long an exposure will blow out highlights more easily due to the small well sizes and the high sensitivity of these sensors. It will also result in all white star colours easily.

So shorter exposures are better and no 20 minute exposures unless you are doing dim narrowband.

QE is massive and still high in narrowband compared to CCD. Its past most CCDs by 40% or more.

Binning 2x2 could also be useful for the small file sizes and somewhat increased signal with very little loss of resolution.

The sensor is very small so field of view is limited so I use this sensor mostly for galaxy imaging or smaller nebulas at 1260mm focal length
(AP Honders Riccardi 305mm F3.8). It works well.

Small pixels also means more sensitive to seeing.

Greg.
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  #22  
Old 25-07-2020, 06:51 AM
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seeker372011 (Narayan)
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Quote:
Originally Posted by gregbradley View Post
I didn't realise til after this post your have the QHY183. I was writing about the ASI183. They seem to require different settings which is odd as they use the same sensor but that's the way it is.

Greg.
Yes thanks. I was aware of that of course. At the moment I am still trying to find the sweet spot but have gain cranked up quite high (25) for H alpha imaging in suburban skies and Offset 11.
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  #23  
Old 25-07-2020, 08:46 AM
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Yeah my only advice with any of these CMOS cameras is not to get too complicated otherwise you'll have a million files for every possible combo to do calibration.

Sky X does not record the gain or offset or any other variable in its files, at least with my pre-subscription version.

So you have to put it in the file name otherwise later when you go to calibrate with several possible combinations of temperature, gain, offset, modes it could become a guessing game. Especially when you do a HaLRGB run and the Ha is done at the same gain as the LRGB or vice versa.

Greg.
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  #24  
Old 25-07-2020, 10:11 AM
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seeker372011 (Narayan)
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Luckily I am using NINA- and it records gain offset and even RMS error in guiding in the file name of you choose to


Loving this software


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Originally Posted by gregbradley View Post
Yeah my only advice with any of these CMOS cameras is not to get too complicated otherwise you'll have a million files for every possible combo to do calibration.

Sky X does not record the gain or offset or any other variable in its files, at least with my pre-subscription version.

So you have to put it in the file name otherwise later when you go to calibrate with several possible combinations of temperature, gain, offset, modes it could become a guessing game. Especially when you do a HaLRGB run and the Ha is done at the same gain as the LRGB or vice versa.

Greg.
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