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ASI2600MC Pro – Gain 0 vs. 100?

astrophotography CMOS imaging
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#51 buckeyestargazer

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Posted 29 August 2020 - 02:18 PM

How they "look" is a good measure as far as I'm concerned, but in the interest of "science" I'll take a look at those stacks for ya. I'll get back to you on this.

Don't go out of your way. It's not a big deal.

#52 PilotAstronomy

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Posted 29 August 2020 - 02:49 PM

Side note:

 

Anyone got an idea of the "ideal" ADU (exposure length) for this camera? I'll admit I'm not as smart as I'd like to be on all the math and how it works as I'd like to be.

 

I ran Shaprcap sensor analysis and got this:

Gain Setting | e/ADU   |  Read Noise (e) | Full Well (e) | Relative Gain | Rel. Gain (db) | Dynamic Range (Stops)
0            | 0.7779  |   3.54759728    | 50978.17943   |        1      |      0         |   13.81074999
100          | 0.2558  |   1.510820115   | 16761.31082   |   3.04141961  |  9.661526837   |   13.43751546

Offset of 50 gives me an ADU of ~500 on a "bias" frame (or any short-exposure dark at 0C).

 

 

I've been shooting 100 gain, 50 offset, 60 seconds and getting an ADU in the 1500-1800 range in my Bortle 4-5 skies. I see a lot of people shooting 180 seconds at 100 gain and getting fine results. I doubt everyone has that much darker skies than I do. Am I over or under-exposing?

 

My previous experience was with the ASI1600 and I often aimed for shorter exposures, and lots of them. If I took a similar approach with this camera as I did before, my exposures should be closer to 15 seconds. I'm unwilling to go lower than 60 seconds due to the overhead lost. Am I using the wrong approach with this camera?

See here for a 361x60second, 100 gain, 50 offset image after processing: https://www.facebook...108167775219790

 

And here for 67x180second, 0 gain, 50 offset: https://www.facebook...108167502107110


Edited by PilotAstronomy, 29 August 2020 - 04:58 PM.


#53 RichieS

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Posted 30 August 2020 - 10:31 AM

ZWO denies it.

But QHY has one in beta and hitting retail around October.

With that said, I have 0 interest/desire to move to mono. The color is hitting all the right notes.


A guy on Sgl emailed zwo to ask if they intend to release a mono version and they confirmed that they would be.
Richard

#54 sn2006gy

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Posted 30 August 2020 - 11:18 AM

A guy on Sgl emailed zwo to ask if they intend to release a mono version and they confirmed that they would be.
Richard

Cool. More competition is great!

 

I'm not waiting for it either way :)  QHY's will be this year.. if ZWO hasn't even started it won't be until next year and even then very limited supply.

 

Every day I use the 2600mc pro, I wonder why people are so anxious for the Mono. There is absolutely nothing I would gain. The amount of signal/detail i'm getting by using modern OSC techniques is absolutely on par or even better with everything i'm seeing from people with monos and much more expensive gear/set ups..   (my current imaging gear is being swapped out for ones in my sig... which can only make it better)

 

I'm not done with my Abell 95 - but this is only 9 hours

 

If i get another 5.5 hours on a new moon, i can blast out the OIII/SII blue as well and my image with 15 hours integration time will be just as good as anything I can find online no matter how i tweak it - pop out more blue? ok... pop out more red? change of curves. The fact is, this OSC is capturing signal and doing things that Mono imagers keeps saying aren't good enough or can't be done but reality isn't reflecting that.

 

BUT... this is me :)  As i say a million times over, you do you!  I am thrilled that APS-C and Full Frame are making headway - our industry NEEDS to get up with the times and adapt or it will die a slow painful into expensive boutique.  At this point in time i care less about Mono/OSC - these new sensors and ways to integrate your data with modern software and techniques is revolutionary period.

 

abell 85 take2

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#55 Dean J.

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Posted 30 August 2020 - 12:07 PM

A guy on Sgl emailed zwo to ask if they intend to release a mono version and they confirmed that they would be.
Richard


Excellent, I intend to be one of the first in line. :-)

#56 ZL4PLM

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Posted 05 September 2020 - 02:27 AM

Anyone hear about a potential ASI2600MM mono camera coming to market any time soon?

its coming as per ZWO's FB post this week but the sensors haven't been released yet for tests ...  it will be next year I guess when they get a chance to get one into a camera



#57 Dean J.

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Posted 05 September 2020 - 09:03 AM

its coming as per ZWO's FB post this week but the sensors haven't been released yet for tests ...  it will be next year I guess when they get a chance to get one into a camera

I may as well get in line for the QHY version then.  They are supposed to be released in October.



#58 ZL4PLM

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Posted 05 September 2020 - 11:49 PM

I may as well get in line for the QHY version then.  They are supposed to be released in October.

I doubt its any diff from ZWO - the manufacturer hasnt released them so I am sure they will be in the same boat - I take release dates from anyone with a pinch of salt these days with COVID affecting everything 



#59 Dean J.

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Posted 06 September 2020 - 01:03 AM

Ask ZWO to give us a release date.  QHY has said October.  There must have been some reason QHY said October.  I would like to continue to use ZWO cameras but if QHY releases their camera and ZWO hasn’t given us some idea of how long we have to wait, then I will go with the QHY268M.



#60 PilotAstronomy

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Posted 06 September 2020 - 09:51 AM

A new camera is a nice topic but what about 0 vs 100 gain and the suggested minimum ADU discussion?

#61 Dean J.

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Posted 06 September 2020 - 10:13 AM

Gain 100, offset 50



#62 PilotAstronomy

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Posted 06 September 2020 - 12:32 PM

Minimum ADU to swamp noise?



#63 Dean J.

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Posted 06 September 2020 - 04:19 PM

Check out the ASI1600 threads from a couple of years ago.  Jon Rista did several excellent explanations on how to calculate exposure levels.



#64 Umasscrew39

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Posted 06 September 2020 - 06:13 PM

Unfortunately, this topic has gone off on several tangents.  The thread Dean is referring to is located here.  You can also determine this yourself using SharpCap for your camera under your sky conditions.  The SharpCap sensor analysis and smart histogram are used to determine the threshold where shot noise is higher than read noise.  The relationships between gain, e/ADU, read noise, and DR are all used to determine exposure levels.  So you can determine the "swamp" the read noise, so that having longer exposures won't significantly improve your signal-to-noise ratio per sub.  The sensor analysis provided by ZWO for this camera is already loaded in SharpCap but you can perform it yourself.  Also Robin Glover (SharpCap author) has a couple of online videos here and here that explain this along with the math.  

 

This thread also took a turn on star saturation and star color of 0 vs.100 gain.  I use 100 gain/50 offset and there is no star saturation.  It was also discussed that star color is gone.  I admitted not much color was in some of my images but I also had a misstep in my processing. Frankly, when I went back a looked at them again, there is indeed blue, red, yellow but mostly white stars. Of course, color will vary based on the object being imaged along with your setup and processing skills. However, my point is that 100 gain with this camera by no means washes out star color nor causes star saturation.  I confirmed all of this with a one hour one on one video conference with Adam Block where we actually went through some of my ASI2600MC images.  He spotted the color immediately and had a few suggestions as to how to bring it out a little more but did not feel gain, exposure time, or filters had much to do with it.  We went into much further detail on the approaches but this should be a topic for discussion.

 

I hope some of this helps and does not add to any confusion.



#65 Ted Dobosz

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Posted 08 September 2020 - 09:08 AM

I have always run my cameras at unity gain, whether it is my ASI2600MC or ASI294MC. I have never really had much trouble with star colors.  Yes there may be a few very bright stars that end up getting saturated but mostly the color is retained for the majority of stars. Post processing usually sorts out a seemingly lack of color, however I have been known to also kill the color in the stars in my processing.. LOL  Even 5 minutes subs can retain colors in the majority of stars.

 

Ted


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#66 Swordfishy

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Posted 11 September 2020 - 12:28 PM

I have the same camera, and after having done all this same research--Gain 100, Offset 50. :-)

 

Highly recommended reading: https://daleghent.co...g-camera-offset

Not to rehash an old thread but it it too good not to bump it up! Excellent read. Ty! 



#67 dghent

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Posted 11 September 2020 - 01:08 PM

I have always run my cameras at unity gain, whether it is my ASI2600MC or ASI294MC. I have never really had much trouble with star colors.  Yes there may be a few very bright stars that end up getting saturated but mostly the color is retained for the majority of stars. Post processing usually sorts out a seemingly lack of color, however I have been known to also kill the color in the stars in my processing.. LOL  Even 5 minutes subs can retain colors in the majority of stars.

It's a very different world when it comes to sensors that sport LCG/HCG modes, so the old standby of "just shoot at unity gain" that is the norm in single gain domain sensors doesn't realistically apply. On some cameras, such as the 2600MC, there is no possible way to get 1e- per ADU and the closest you can get to it means you're you are going to suffer from maximum read noise that is at a level that is 3x what you would get otherwise. Here, in astrophotography applications, the game is minimizing read noise while maximizing dynamic range, and this generally happens right where the sensor switches into HGC mode at our illumination levels. Photometrists will of course desire deeper wells and so such applications would largely exist in the LCG domain where well depth is the deepest.

 

If you want to read a scholarly paper on the subject, check out this dissertation: MOSFET Modulated Dual Conversion Gain CMOS Image Sensors (Xiangli Li) starting around page 42 onwards.


Edited by dghent, 11 September 2020 - 01:11 PM.

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#68 Jon Rista

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Posted 11 September 2020 - 02:59 PM

Side note:

 

Anyone got an idea of the "ideal" ADU (exposure length) for this camera? I'll admit I'm not as smart as I'd like to be on all the math and how it works as I'd like to be.

 

I ran Shaprcap sensor analysis and got this:

Gain Setting | e/ADU   |  Read Noise (e) | Full Well (e) | Relative Gain | Rel. Gain (db) | Dynamic Range (Stops)
0            | 0.7779  |   3.54759728    | 50978.17943   |        1      |      0         |   13.81074999
100          | 0.2558  |   1.510820115   | 16761.31082   |   3.04141961  |  9.661526837   |   13.43751546

Offset of 50 gives me an ADU of ~500 on a "bias" frame (or any short-exposure dark at 0C).

 

 

I've been shooting 100 gain, 50 offset, 60 seconds and getting an ADU in the 1500-1800 range in my Bortle 4-5 skies. I see a lot of people shooting 180 seconds at 100 gain and getting fine results. I doubt everyone has that much darker skies than I do. Am I over or under-exposing?

 

My previous experience was with the ASI1600 and I often aimed for shorter exposures, and lots of them. If I took a similar approach with this camera as I did before, my exposures should be closer to 15 seconds. I'm unwilling to go lower than 60 seconds due to the overhead lost. Am I using the wrong approach with this camera?

See here for a 361x60second, 100 gain, 50 offset image after processing: https://www.facebook...108167775219790

 

And here for 67x180second, 0 gain, 50 offset: https://www.facebook...108167502107110

 

 

FWC determines maximum exposure length. So, while both of those settings have roughly the same DR, one has a significantly smaller FWC than the other. That WILL affect how long you can expose. If you WANT longer exposures, which is perfectly fine (and when you are facing stacking tons of 60 second exposures, is quite beneficial), then use the lower gain, and use longer exposures. The same general rules of exposure apply...you would want to swamp the read noise by a sufficient amount with either gain.

 

By my calculation, based on your read noise numbers, 3.55^2/1.52^2 means you could expose up to 5.5x longer at the lower gain. Well, more specifically, to swamp the read noise by the same ratio, you would NEED to expose 5.5x longer. So if you are using 60 second subs at Gain 100, then you would be using 330 second subs at Gain 0. This all assumes that you are swamping the read noise by the right amount at 60 seconds @ gain 100. If you are swamping more than you need to, you could still use shorter subs at Gain 0...if you are not swamping enough, you may need even longer subs at Gain 0.

 

This is one area where the multi-modal design of the QHY600 can be beneficial. One of its modes supports around an 80ke- FWC at minimum gain, which allows for longer exposures. 


Edited by Jon Rista, 11 September 2020 - 03:02 PM.

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#69 PilotAstronomy

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Posted 11 September 2020 - 08:16 PM

Thanks, Jon. With this camera how do I know I’m hitting the minimum exposure to swamp read noise? Specifically at what ADU? I was using the charts in the threads referenced above for my ASI1600 to great effect but this camera will be a bit different math and I’ve always struggled to wrap my head around the math.

#70 skyman1975

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Posted 13 September 2020 - 11:08 AM

Hi!

This is just a test. Single shot, 500s,. Takahashi TSA 102S F6.

ASI2600M.

 

Gain 100,  Offset 50, -10C
No darks, no bias, no flats.

Bortle: 3.00 Gran Canaria (Spain)
Basic Pixinsight

 

get.jpg?insecure


Edited by skyman1975, 13 September 2020 - 11:10 AM.

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#71 sn2006gy

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Posted 13 September 2020 - 03:38 PM

Hi!

This is just a test. Single shot, 500s,. Takahashi TSA 102S F6.

ASI2600M.

 

Gain 100,  Offset 50, -10C
No darks, no bias, no flats.

Bortle: 3.00 Gran Canaria (Spain)
Basic Pixinsight

 

get.jpg?insecure

 

looks great! I wish i could get me some bortle 2-3 skies ;)



#72 poolemarkw

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Posted 11 February 2021 - 11:25 AM

Hi Everyone,

 

I'm shooting from Bortle 5-6 skies, and it appears that the recommendation is Gain = 100 and Offset = 50 regardless of exposure length.   Is that correct?  It seems that with shorter exposures the histogram will be so far to the left that you can't process it very well.  What am I missing?

 

Mark



#73 sn2006gy

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Posted 11 February 2021 - 12:58 PM

Hi Everyone,

 

I'm shooting from Bortle 5-6 skies, and it appears that the recommendation is Gain = 100 and Offset = 50 regardless of exposure length.   Is that correct?  It seems that with shorter exposures the histogram will be so far to the left that you can't process it very well.  What am I missing?

 

Mark

 

Hi Mark,

 

a lot has changed for me since this topic started ;) i'm now in B1 skies and loving it.

 

With most scopes faster than f7 and shooting broadband, you'd be hard pressed to worry about histogram being too far left.

 

For many, it comes down to how much data you want to work with. For example, in broadband at gain 100 I took 1000 subs and that's a lot for Pixinsight to process, but at gain 0 I took 350 and that's more manageable.   I'm fine with large integrations so I typically shoot at gain 100 and just let processing rip overnight.

 

With NB imaging, 5 minute subs work great with duo/trio/quad filters but may need longer with dedicated narrow filters.. not so much a problem. Shoot at higher gain here.



#74 TelescopeGreg

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Posted 12 February 2021 - 10:53 PM

Ok, so a sanity check...

 

I've got a 130mm f/7 scope, no reducer.  Bortle 6 here.  My imaging sweet spot seems to be 4 minute subs (or less), but to get the proverbial histogram peak barely off the left edge I seem to need up the gain to about 300.  Is that about right?

 

Compared to gain 100 (or 0) I know I'm reducing the dynamic range (fortunately the camera has a lot to start with), but the alternative appears to require a much longer exposure at gain 100, far longer than my mount and patience can support.  An f/7 scope isn't exactly fast, but it's not exactly slow, either.

 

I just found the exposure spreadsheet, but haven't had a chance to wade through it.  In the mean time, is my exposure sane?



#75 Wow!

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Posted 13 February 2021 - 08:21 PM

^ Keen to hear the answers to this as well, as I'm someone looking to buy both a 2600MC and a 130 f/7 refractor.

I live under B7 skies, but also shoot at B3 on weekends.




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