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QHY183M First Light Field Notes & Image: NGC 6946 LRGBHa

astrophotography CMOS dso equipment imaging refractor
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#1 BenKolt

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Posted 04 August 2020 - 09:46 AM

Greetings!

 

I have completed my first image and processing using my new QHY183M CMOS.  This is also my very first use of a CMOS as all my experience has been with CCD cameras.  It was my wish to evaluate how well I could use a small pixel CMOS on a mid-range focal length refractor to achieve resolution that was commensurate with using larger pixel CCDs on longer focal length scopes.  The result turned out fairly well.

 

On the AstroBin page I provide a lot more details including field notes with using the QHY183M with SGP as well as choices made on offset, gain, exposure times, etc.  Please follow the links to the AB pages for those details and feel free to comment here or there.

 

Higher Resolution AstroBin Links:

Thank you for your attention, and your comments and suggestions are most welcome!

 

Best Regards,

Ben

 

 

This is a cropped version of the image that hasn't reproduced well here on CN.  I recommend that you take a look at the higher resolution images on AB for a more fair evaluation.

 

NGC6946_LRGB_123-01-05_1x1_0030s_20200710_-20C.v005E_C1-1.jpg

 

 


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#2 BenKolt

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Posted 04 August 2020 - 09:47 AM

Here is the wide field of view that better represents what the full sensor was able to image.  Only minimal crop done here.

 

NGC6946_LRGB_123-01-05_1x1_0030s_20200710_-20C.v005A_LRGB-1.jpg

 

 


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#3 Jeff2011

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Posted 04 August 2020 - 01:03 PM

Very nice Ben.  How did you come to choose 30 second exposures for LRGB?  

 

I recently ordered a QHY5LIII178M guide camera to replace my aging QHY5L-IIm.  In my case I will be binning but I look forward to my guide camera no longer randomly disconnecting on me and a bigger and more sensitive sensor.



#4 BenKolt

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Posted 04 August 2020 - 01:19 PM

Very nice Ben.  How did you come to choose 30 second exposures for LRGB?  

 

I recently ordered a QHY5LIII178M guide camera to replace my aging QHY5L-IIm.  In my case I will be binning but I look forward to my guide camera no longer randomly disconnecting on me and a bigger and more sensitive sensor.

Thanks, Jeff.  I had come by a chart somebody put together showing optimal exposure times for different sky glow conditions (and now I can't find it anymore).  This was done for the ASI version of this camera.  I had to make a couple of estimations to arrive at 30s exposures, but I'm now thinking I should have actually used a smaller exposure.  Ideally, I'd like to generate my own numbers based on more accurate measure of gain, read noise and my own evaluation of sky flux and target flux from objects of interest, but in the AB notes I describe some problems I ran into in measuring offset, which I need to make a PTC to measure gain and read noise more accurately.  I need to revisit all that.

 

One thing I recognize is that I will always be clipping the brightest of the stars no matter what I do, and this is also the case with my CCD cameras.  For this CMOS camera, at least using the operating parameters that  I chose for this image, I seem to be clipping even more so than with the CCDs.  I have not optimized this yet.

 

Ben



#5 terry59

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Posted 04 August 2020 - 05:55 PM

That is a nice image. I had recently decided to use my 183M strictly for narrowband....I think I'll stick with that plan



#6 AtmosFearIC

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Posted 04 August 2020 - 07:29 PM

I have a QHY183M that I use at Gain 4 which used the full 12-stops of dynamic range. If you’re shopping at F/7 under dark skies you should be using closer to 300s rather than 30s. It does all depend on what gain you’re using but 30s is too short for any F/7 telescope.

Edited by AtmosFearIC, 04 August 2020 - 07:34 PM.


#7 BenKolt

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Posted 04 August 2020 - 08:11 PM

That is a nice image. I had recently decided to use my 183M strictly for narrowband....I think I'll stick with that plan

Thank you Terry!



#8 BenKolt

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Posted 04 August 2020 - 08:14 PM

I have a QHY183M that I use at Gain 4 which used the full 12-stops of dynamic range. If you’re shopping at F/7 under dark skies you should be using closer to 300s rather than 30s. It does all depend on what gain you’re using but 30s is too short for any F/7 telescope.

Could you explain this please?  Why is 30s too short for any F/7 telescope?  Thanks!

 

(I'm not shooting under dark skies, by the way, rather suburban skies ...)



#9 AtmosFearIC

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Posted 04 August 2020 - 10:40 PM

https://www.astrobin.../full/3zcxwa/0/

This was shot with an 8” F/3 under Bortle 6 skies with 60s RGB. The exposures were longer than I needed but made it easier than short ones. That’s at F/3 however. I think I am RN limited at 5-10s in luminance. At F/7 that equates to 30-60s with luminance and RGB should be approx 3x that.

#10 BenKolt

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Posted 05 August 2020 - 07:40 PM

https://www.astrobin.../full/3zcxwa/0/

This was shot with an 8” F/3 under Bortle 6 skies with 60s RGB. The exposures were longer than I needed but made it easier than short ones. That’s at F/3 however. I think I am RN limited at 5-10s in luminance. At F/7 that equates to 30-60s with luminance and RGB should be approx 3x that.

 

AtmosFearIC:

 

Thank you.  That's very nice.  You did not record gain settings on the AB page, however.  What did you use here?

 

Last night I had opportunity to do some imaging on another target, and I used the near full moon night to play around with many differing luminance exposures and a gain parameter setting of 4, which corresponds to higher gain value of about 2 e-/ADU, near max full well and near max dynamic range.  I think I'm going to like this setting more.  I haven't done a detailed analysis of the results yet, but it looks to me that I can at least achieve the same level of star saturation per frame that I did here, but now with exposures on the order or 3 - 4 min instead of 30s.  But 10 min exposures as you originally suggested is too long for my skies for broadband, certainly for the luminance filter.

 

For this image I used a gain of about 0.5 e-/ADU (gain parameter of 16) with exposures of 30s, and I'm understanding better now how this likely did not let me utilize the camera to its fullest performance capabilities.

 

Incidentally, I came across this link with nice product details about the QHY183M.

 

Best Regards,

Ben



#11 AtmosFearIC

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Posted 05 August 2020 - 09:01 PM

AtmosFearIC:

 

Thank you.  That's very nice.  You did not record gain settings on the AB page, however.  What did you use here?

 

Last night I had opportunity to do some imaging on another target, and I used the near full moon night to play around with many differing luminance exposures and a gain parameter setting of 4, which corresponds to higher gain value of about 2 e-/ADU, near max full well and near max dynamic range.  I think I'm going to like this setting more.  I haven't done a detailed analysis of the results yet, but it looks to me that I can at least achieve the same level of star saturation per frame that I did here, but now with exposures on the order or 3 - 4 min instead of 30s.  But 10 min exposures as you originally suggested is too long for my skies for broadband, certainly for the luminance filter.

 

For this image I used a gain of about 0.5 e-/ADU (gain parameter of 16) with exposures of 30s, and I'm understanding better now how this likely did not let me utilize the camera to its fullest performance capabilities.

 

Incidentally, I came across this link with nice product details about the QHY183M.

 

Best Regards,

Ben

I only use a Gain of 4 and leave it there :)

For some reason I thought you'd mentioned that you were under dark skies but light pollution makes such a big difference!

 

From the graphs on that page it shows that a Gain of 4 gets the most dynamic range out of the camera possible as it only has a 12-bit ADC. The difference between Gain 4 and Gain 16 is really that you can exposure 4x longer before saturating while only needing a 75% increase in time to swamp read noise and gaining nearly 1.5 stops of dynamic range.



#12 BenKolt

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Posted 05 August 2020 - 10:00 PM

I only use a Gain of 4 and leave it there smile.gif

For some reason I thought you'd mentioned that you were under dark skies but light pollution makes such a big difference!

 

From the graphs on that page it shows that a Gain of 4 gets the most dynamic range out of the camera possible as it only has a 12-bit ADC. The difference between Gain 4 and Gain 16 is really that you can exposure 4x longer before saturating while only needing a 75% increase in time to swamp read noise and gaining nearly 1.5 stops of dynamic range.

That's right.  The fog is clearing on my understanding.  Thanks again.




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