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Old 27-06-2020, 06:19 PM
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QHY 183 MM gain and offset settings -your advice please

Hi all


After some deliberation and after considering the advice from people on this forum and CN I finally decided to go with a QHY 183M

I was able to take it it for a spin a couple of days ago. I used a Baader 7nm H alpha Filter so this was a narrow band imaging test.

I started with the recommended gain and offset of 8 and 11 respectively but could see no image preview in NINA or in SharpCap. I tried testing if this was an autostretch issue by tempting to plate solve a saved image but failed at these settings and various other test exposures in both NINA and also in All Sky Plate Solver.

Finally I cranked the gain up to 30- which is I understand Is well into the digital gain region and a big no-no ( from a thread in CN) , but was able to plate solve and grab an image but dark calibration was very poor with lots of amp glow residual and I suspect clipping in the shadows. I also tried Nebulosity 4 as capture software and again needed to crank up the gain quite a bit

Havenít been able to take the system out again to try further because of weather but in the interim, I wonder if any one who uses this camera with a narrow band filter -ideally H alpha -would please share your settings?


if you are using SharpCap as well with this camera and a narrow band filter it would be good if you could share those settings as well- not sure if there is any reason the settings for NINA and SharpCap would be different but who knows.


thanks in advance


Narayan
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Old 27-06-2020, 08:50 PM
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Hi Narayan . I have the ASI 183mc which i assume is similar. For lots of 2- 3minute images to stack In DSS it works well at 75 gain and the standard 8 offset. I imaged the triffid that way.

The best way to start with DS images.

You can go a higher I think but it gets noisy.

An enjoyable feature of these cameras is the ability to do a live feed in RGB24 for bright objects or use a live stack in Sharpcap using 16 bit mono so you can see what the colour result might be within a few minutes. For that live stack EAA however you need a high gain of say 270 and a short exposure of 8 seconds and set RGB balance to auto so it looks ok. There are tutorials for this on the net. You can see the Centaurus A galaxy clearly within a few minutes .

Last edited by Sunfish; 27-06-2020 at 09:28 PM. Reason: Name
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Old 27-06-2020, 08:53 PM
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Ps. You can add a Ha filter to the DSS stack images also at 75 gain but also get a stack without the filter. I used 7nm filter but 12nm or more is common.
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Old 27-06-2020, 09:51 PM
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I had the ASI 183MM for a while....
I do solar imaging. The unity gain is 120 for this camera. That's what I used under FireCapture - no offset applied.
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Old 27-06-2020, 09:58 PM
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I think I’m using a gain of 3-4 and an offset around 5 but I’d have to check my laptop but it’s around these figures.
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Old 27-06-2020, 10:11 PM
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Sorry Narayan,
I was replying to a previous post regarding a 183c so perhaps a much lower gain would be correct for the 183m . Did you try a daytime gain test on a distant object to see how the histogram looks?. I tried that with my 1600m with and without the Ha filter.
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Old 27-06-2020, 11:10 PM
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Quote:
Originally Posted by Sunfish View Post
Sorry Narayan,
I was replying to a previous post regarding a 183c so perhaps a much lower gain would be correct for the 183m . Did you try a daytime gain test on a distant object to see how the histogram looks?. I tried that with my 1600m with and without the Ha filter.
I think there is a factor of 10 between the Zwo and the QHY Cameras so the ZWO settings translate to a gain of 7.5 or 8 which is pretty much what QHY recommends - and which doesnít seem to be working. No I havenít tried to look at the histogram in the daytime yet but will do so. Thanks
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Old 27-06-2020, 11:11 PM
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I think I’m using a gain of 3-4 and an offset around 5 but I’d have to check my laptop but it’s around these figures.
Thanks for the response.

Gosh that seems really low compared to the recommended QHY starting gain and offset-is that with a narrow band filter?
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Old 27-06-2020, 11:14 PM
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Quote:
Originally Posted by Merlin66 View Post
I had the ASI 183MM for a while....
I do solar imaging. The unity gain is 120 for this camera. That's what I used under FireCapture - no offset applied.

That translates to a 12 gain for a QHY with 0 offset - but I suppose daytime imaging may not be strictly comparable. Thanks for the response
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Old 28-06-2020, 08:56 AM
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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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Old 28-06-2020, 10:44 AM
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Quote:
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.

Thanks for the detailed response Greg.
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  #12  
Old 29-06-2020, 12:12 PM
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How to Scientifically Determine CCD Gain and Offset Settings
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Old 29-06-2020, 12:33 PM
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Iím pretty sure the QHY 183 is a CMOS camera not a CCD.
Different anaimal.
Buil has done some work on CMOS vís CCD.
Iíll find and post the link.
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Old 29-06-2020, 12:43 PM
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I checked my astro laptop last night and I’m using a GAIN of 4 and Offset of 7. This gives around 1.9e RN (I’d have to go back and check my notes) and 12 bits fo dynamic range which matches the 12 bit ADC.
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Old 29-06-2020, 03:21 PM
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https://www.atik-cameras.com/news/cm...ngs-explained/


Worth watching.....
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Old 29-06-2020, 05:17 PM
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Thanks for this


QHY themselves sent me some information as well:

https://www.qhyccd.com/uploadfile/20...6030334403.pdf
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Old 29-06-2020, 05:18 PM
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Thatís a fantastic video, thanks !
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Old 29-06-2020, 05:19 PM
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I checked my astro laptop last night and Iím using a GAIN of 4 and Offset of 7. This gives around 1.9e RN (Iíd have to go back and check my notes) and 12 bits fo dynamic range which matches the 12 bit ADC.
Thanks for taking the trouble to look it up. Thatís a very low gain setting - is this for RGB or narrow band?
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Old 29-06-2020, 07:01 PM
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Originally Posted by seeker372011 View Post
Thanks for taking the trouble to look it up. Thatís a very low gain setting - is this for RGB or narrow band?
I use it for both, I took some 300s Ha shots of M8 last night along with 60s RGB of M30. Taking 900s SII of NGC 6188, 300s of NGC 3195 Ha tonight.
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Old 30-06-2020, 09:50 AM
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Thanks for this




QHY themselves sent me some information as well:

https://www.qhyccd.com/uploadfile/20...6030334403.pdf

Thanks for the link... didn't have that document.
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