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Sony IMX183 mono test thread - ASI, QHY, etc.

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#1001 Jon Rista

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Posted 18 June 2019 - 04:34 PM

Nice, Steven.  I've found that dark current just isn't an issue with the 183MM Pro.  Neither is amp glow smile.gif

 

I'm curious, though -- specs say gain 120 is "unity."  I know 111 isn't far off, but did you use a different source to get the 111 figure as "unity?"  Other than the ASI specs, I mean...?

I'm pretty sure 111 is unity. My own testing has shown that at gain 111, the conversion ratio is ~1e-/ADU (very slightly more, like 1.01...e-/ADU). Gain 120 would be a bit higher than unity. 


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#1002 BillMc

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Posted 18 June 2019 - 05:22 PM

Unity Gain is 111

 

I raised the discrepancy in the manual with ZWO in this topic:

 

https://bbs.astronom...opic.php?t=8325

 

Bill


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#1003 StevenBellavia

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Posted 21 June 2019 - 10:46 AM

Nice, Steven.  I've found that dark current just isn't an issue with the 183MM Pro.  Neither is amp glow smile.gif

 

I'm curious, though -- specs say gain 120 is "unity."  I know 111 isn't far off, but did you use a different source to get the 111 figure as "unity?"  Other than the ASI specs, I mean...?

I carefully matched the 8 points off their published curve. 

 

I ignored the "Gain 120" with the arrow.

 

Using an exponential least-squares regression, I fitted the 8 points and also filled in all the points in-between, every 10 units of Gain (0.1 db per 1 unit of gain for ZWO).

 

If you use that least squares regression equation, at Gain 111, you get 1.01 e/ADU

 

Since the ASCOM driver refers to unity as 111, I assumed that must be correct. Or at least close enough. 

 

Steve

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Edited by StevenBellavia, 21 June 2019 - 01:48 PM.

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#1004 kmachhi

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Posted 24 June 2019 - 06:15 PM

I recently purchased the ASI183MC-Pro.  I imaged IC4605 (in Rho Ophiuchus) for my first trial with the HDR setting (gain=0) using 120s subs and then also with the unity gain setting (gain=111) using 90s subs.  With both gain settings most of the stars are saturated, I get good details on the nebulosity in the image.  I plan to experiment with the HDR setting and 90s and 60s subs.  Any recommendations on settings that will result in achieving decent star colors with this color camera? 

 

Thanks,

Khushrow



#1005 Jon Rista

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Posted 24 June 2019 - 06:28 PM

I recently purchased the ASI183MC-Pro.  I imaged IC4605 (in Rho Ophiuchus) for my first trial with the HDR setting (gain=0) using 120s subs and then also with the unity gain setting (gain=111) using 90s subs.  With both gain settings most of the stars are saturated, I get good details on the nebulosity in the image.  I plan to experiment with the HDR setting and 90s and 60s subs.  Any recommendations on settings that will result in achieving decent star colors with this color camera? 

 

Thanks,

Khushrow

What are you considering "saturated"? For "most" of the stars to saturate, you would have to be rather wildly overexposed. Even with heavy LP, unless you are imaging at an extremely wide field with a very fast scope or lens, I would expect "some" but definitely not "most" stars to clip at 120 seconds for Gain 0. For more normal scopes, though, with the tiny pixels, and a 15ke- FWC, it should be pretty hard to saturate stars with this camera unless your image scale was 2-3"/px or more and a fairly fast f-ratio. 

 

Are you looking at a stretched image to determine which stars are saturating? Or are you looking at the unstretched linear image? And, when you say "saturated"...are you actually measuring the stars to see if they have indeed saturated (reached maximum signal)...or are you just assuming that every star that is visible in the linear signal field is "saturated"? If the latter...then my guess is only some of the stars you can see in the unstretched image are actually saturated. You can start to see stars in an unstretched sub LONG before they even get close to saturating. Saturation is only when they actually clip at maximum signal.


Edited by Jon Rista, 24 June 2019 - 06:29 PM.


#1006 james7ca

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Posted 25 June 2019 - 03:48 AM

In terms of avoiding saturation, I think you'll need more than a one stop change in exposure. Do at least two stops and then think of gathering subs at two more stops below that to cover a complete range. So, if you are using 120s for the main capture then I'd go for 30s and something around 10 to 5 seconds. You don't really need very many subs at those lower exposures since you only need to capture the brightest parts of the image. When you do an HDR combination in a program like PixInsight it will mask out everything except the bright threshold that you set as part of the HDR process. Thus, the short integration times that you use for the lower exposures won't really affect the background signal-to-noise.

 

Gain certainly affects dynamic range, but I even do HDRs on some of my narrow-band captures (at least if I plan on doing something like a bi-color combination). I should also add that you obviously don't want to reduce your exposure time to the point were you could have too few stars to do your registration/alignment during the processing.

 

IMO, one of the greatest failings of many color images (including narrow band) is that they fail to show any color in the stars.


Edited by james7ca, 25 June 2019 - 12:08 PM.

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#1007 Ethanwyh

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Posted 20 September 2019 - 03:37 AM

Hi all, would like to get a general consensus on the QHY183M Gain and Offset settings:

 

For 'best' results

 

For LRGB: Gain=?; Offset=?

For Narrowband: Gain=?; Offset=?

 

Do let me know based on your experiences :D

 

P.S Bortle 7 skies; F/7.5 80mm Aperture with Ha=6.5nm, Sii-7nm, Oiii=7nm if that helps

 

 

Cheers!



#1008 Ethanwyh

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Posted 20 September 2019 - 03:44 AM

I have been enjoying my QHY183M.  Have an amazing clear night Friday night (they are rare) so I imaged the the Flame/Horsehead nebula in narrowband

 

The first one is in Ha

get.jpg?insecure

 

The second one is combine (HSO)

get.jpg?insecure

Hi Mike, what GAIN and OFFSET settings were you on for each subs? It's pretty impressive!



#1009 terry59

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Posted 20 September 2019 - 06:19 AM

Hi all, would like to get a general consensus on the QHY183M Gain and Offset settings:

 

For 'best' results

 

For LRGB: Gain=?; Offset=?

For Narrowband: Gain=?; Offset=?

 

Do let me know based on your experiences laugh.gif

 

P.S Bortle 7 skies; F/7.5 80mm Aperture with Ha=6.5nm, Sii-7nm, Oiii=7nm if that helps

 

 

Cheers!

I am using gain 11 offset 30 for NB


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#1010 StarMike8SE

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Posted 20 September 2019 - 08:33 AM

Hi Mike, what GAIN and OFFSET settings were you on for each subs? It's pretty impressive!

I set the gain slider 2/3s the way up and the offset 1/3



#1011 StarMike8SE

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Posted 20 September 2019 - 08:35 AM

Got this of the Eastern crescent Nebula Tuesday night

 

 get.jpg?insecure



#1012 terry59

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Posted 20 September 2019 - 09:28 AM

I've just started getting data with mine and have only a Ha filter. Here is one and I've put another on astrobin 

 

https://astrob.in/69hem5/0/

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#1013 bobzeq25

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Posted 20 September 2019 - 10:19 AM

What are you considering "saturated"? For "most" of the stars to saturate, you would have to be rather wildly overexposed. Even with heavy LP, unless you are imaging at an extremely wide field with a very fast scope or lens, I would expect "some" but definitely not "most" stars to clip at 120 seconds for Gain 0. For more normal scopes, though, with the tiny pixels, and a 15ke- FWC, it should be pretty hard to saturate stars with this camera unless your image scale was 2-3"/px or more and a fairly fast f-ratio. 

 

Are you looking at a stretched image to determine which stars are saturating? Or are you looking at the unstretched linear image? And, when you say "saturated"...are you actually measuring the stars to see if they have indeed saturated (reached maximum signal)...or are you just assuming that every star that is visible in the linear signal field is "saturated"? If the latter...then my guess is only some of the stars you can see in the unstretched image are actually saturated. You can start to see stars in an unstretched sub LONG before they even get close to saturating. Saturation is only when they actually clip at maximum signal.

Pretty close, but, as a practical matter, my experience is somewhat different.  At high speed, the field doesn't have to be _that_ wide, and the image scale numbers you cite could be somewhat misleading.

 

With my F2 RASA, I can saturate "too many" stars for my taste with a 183color (which is harder to saturate) at 20", gain 50.  (Some guy I know here suggested lower gains could be trouble, and his advice is generally excellent.  <smile>)  1.2 image scale.

 

This is pretty marginal, and it's 150X15".

 

https://www.astrobin...3196/B/?nc=user

 

And yes, "too many" stars are saturated in individual subs.  Not that I know how to fix saturated stars in final images without complicated HDR techniques.  <smile>


Edited by bobzeq25, 20 September 2019 - 10:37 AM.



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