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Building a Dark Library Question?

astrophotography CMOS
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#1 Jim Waters

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Posted 25 March 2020 - 08:37 PM

I received my ASI2600MC Pro today and as expected its cloudy.  I started building a Dark Library.  I completed 120 and 180 seconds using unity gain and started on 60 seconds.  For now I will be using a 90mm triplet f/5.6 scope.

 

What exposure times are users using to build their Dark Library? 


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#2 jmorales21

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Posted 25 March 2020 - 08:43 PM

I received my ASI2600MC Pro today and as expected its cloudy.  I started building a Dark Library.  I completed 120 and 180 seconds using unity gain and started on 60 seconds.  For now I will be using a 90mm triplet f/5.6 scope.

 

What exposure times are users using to build their Dark Library? 

The same exposures and temperatures that you plan to use when exposing your "lights". 

 

So if you plan on using 10m, 20m and 30m at -20C or -10C, you will have to make different sets that match those conditions.

 

Cheers,

 

Jose


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#3 dghent

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Posted 25 March 2020 - 08:45 PM

I start at 30 seconds and go to 300 seconds (5 minutes) in 30 second intervals, then after 300 seconds I go to 10 minutes in 1 minute intervals. 

 

I take 30 frames at each interval. Yes, it takes a long time, but that's what cloudy weekends are for.


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#4 Jim Waters

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Posted 25 March 2020 - 10:03 PM

Thanks jmorales21 and dghent.



#5 ezwheels

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Posted 25 March 2020 - 10:12 PM

Same as dghent. I also just pick a temperature that I can easily get the chip down to in warmer months and I can use the library all year round. This is especially so with this chip and its siblings, as they have near zero dark current at even 0C and -5C. 



#6 Peter in Reno

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Posted 25 March 2020 - 10:26 PM

Since this camera does not produce amp glows, you may only need one Master Dark and use dark scaling or optimization. This will greatly save hard disk spacing for not having multiple darks of different temperatures or sub-exposure times. If you are not familiar with dark scaling, please do a Google search. 

 

https://www.pixinsig.../master-frames/

 

Peter 


Edited by Peter in Reno, 25 March 2020 - 10:42 PM.

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#7 ezwheels

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Posted 25 March 2020 - 10:45 PM

For a OSC CMOS camera the disk space of 10-15 master darks is not so much of a burden. The time to take all the individual subs at each temp, duration, gain and offset adds way up though. As far as dark scaling I have not seen anything about whether this works or not with these new Sony sensors. If it did that would be the way to go to save that time.


Edited by ezwheels, 25 March 2020 - 10:49 PM.

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#8 bobzeq25

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Posted 25 March 2020 - 10:47 PM

Since this camera does not produce amp glows, you may only need one Master Dark and use dark scaling or optimization. This will greatly save hard disk spacing for not having multiple darks of different temperatures or sub-exposure times. If you are not familiar with dark scaling, please do a Google search. 

 

https://www.pixinsig.../master-frames/

 

Peter 

Just an opinion.  I think scaling is an approximation.  If I was building a library, I'd build a library.  <smile>


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#9 Peter in Reno

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Posted 25 March 2020 - 10:53 PM

Just an opinion.  I think scaling is an approximation.  If I was building a library, I'd build a library.  <smile>

Dark scaling works wonderfully with my Sony ICX-694 camera, same sensor as yours.

 

Peter



#10 Jim Waters

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Posted 25 March 2020 - 11:21 PM

Since this camera does not produce amp glows, you may only need one Master Dark and use dark scaling or optimization. This will greatly save hard disk spacing for not having multiple darks of different temperatures or sub-exposure times. If you are not familiar with dark scaling, please do a Google search. 

 

https://www.pixinsig.../master-frames/

 

Peter 

I will check out Dark Scaling.  Thanks



#11 dghent

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Posted 25 March 2020 - 11:36 PM

Dark scaling works wonderfully with my Sony ICX-694 camera, same sensor as yours.

 

The OP's camera is a CMOS, and dark scaling is generally not advisable on CMOS due to amp glow (however little there may be). Amp glow does not scale linearly. Reliable dark scaling is pretty much the domain of CCDs, so I would't blanket-recommend it for everything.


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#12 Peter in Reno

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Posted 25 March 2020 - 11:46 PM

But this particular camera does not produce amp glow and it's a CMOS sensor.

 

https://astronomy-im...600mc-pro-color

 

Scroll down to "Zero amp glow".

 

Since the OP is getting this camera, there's no harm trying dark scaling with this camera and it's really easy.

 

Peter 



#13 dghent

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Posted 25 March 2020 - 11:59 PM

But this particular camera does not produce amp glow and it's a CMOS sensor.

 

https://astronomy-im...600mc-pro-color

 

Scroll down to "Zero amp glow".

 

Since the OP is getting this camera, there's no harm trying dark scaling with this camera and it's really easy.

 

Zero apparent amp glow. Compared to other CMOS sensors, yes, it certainly looks like zero and yeah this looks utterly fantastic for CMOS tech. But I'm kind of circumspect that it is actually, truly zero amp glow like there is zero amp glow with a CCD. In this case, it could still be present, just very well-controlled.


Edited by dghent, 26 March 2020 - 12:00 AM.


#14 Jim Waters

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Posted 26 March 2020 - 12:09 AM

On a related topic any opinions on Offset and Gain?  I will be using a 90mm f/5.6 scope and L-eNhance filter in the city and no filters at my dark-sky site.



#15 dghent

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Posted 26 March 2020 - 12:25 AM

On a related topic any opinions on Offset and Gain?  I will be using a 90mm f/5.6 scope and L-eNhance filter in the city and no filters at my dark-sky site.

Dr. Q of QHY has a write up about gain and offset calculation here:

https://www.qhyccd.c...photography.pdf

 

The other resource you should use are the graphs that ZWO published for the camera:

https://astronomy-im...600mc-pro-color

 

Scroll down to the line graphs under "Camera Performance". You will want to key in the bottom 2 of the 4 graphs they have:

 

graph-of-2600mc-pro-1024x973.png

Unique to this sensor and a few others (IMX455, IMX294) there is a dual-gain mode; high and low. Note that on a typical CMOS sensor, dynamic range (DR) of the sensor drops as gain increases. Read noise decreases. On this sensor, once you turn the gain up past a certain point, the camera switches to a high gain mode where the read noise drops and dynamic range is mostly recovered. This is pretty much a sweet spot of the camera: you get the most DR for the least read noise. For standard DSO astrophotography, you will want to start at this point. So I would guess, start at a gain value of 100, while following Dr. Q's instructions of determining your offset.


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#16 Jim Waters

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Posted 26 March 2020 - 12:45 AM

Thanks for the detailed information and external link dghent.


Edited by Jim Waters, 26 March 2020 - 01:07 AM.


#17 ippiu

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Posted 27 March 2020 - 03:07 AM

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Annotazione 2020-03-27 090656.jpg



#18 buckeyestargazer

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Posted 27 March 2020 - 07:20 AM

Zero apparent amp glow. Compared to other CMOS sensors, yes, it certainly looks like zero and yeah this looks utterly fantastic for CMOS tech. But I'm kind of circumspect that it is actually, truly zero amp glow like there is zero amp glow with a CCD. In this case, it could still be present, just very well-controlled.

You are correct.  There is a very tiny amount of amp glow.  This is a 20min dark at gain 100, auto stretched in Pixinsight.

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  • ASI2600 Amp Glow.jpg

Edited by buckeyestargazer, 27 March 2020 - 07:21 AM.

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