I just had a reply back from ZWO in my image problem
I’m surprised at such a quick reply
Very much appreciated
Quote …
With the ASI2600, ZWO turns on the Sony sensor's High Conversion Gain (HCG) mode at a gain of 100 or above. You should expect the signal to noise ratio of shorter exposures to be about 8 to 10 dB worse when you use a gain of 0 vs when you use a gain of 100. So, changing the gain to zero does make a huge impact on signal to noise ratio, in the case of the ASI2600.
Remember that by using a constant exposure time, your signal drops dramatically with a gain of 0 (0 dB), while the read noise has popped up by more than 3 dB. With a gain of 100 (10 dB, or factor of about 3.16) your signal has not only gone up by a factor of 3.16, but HCG causes the read noise to go down by a factor of more than 2.
If you use really long exposures (30 minutes to 60 minutes), the read noise contribution is less. But at Bortle 7, I suspect that you won't be able to do that, even with a narrow band filter.
You will loose dynamic range with a gain of 100 (but not by much with Sony's HCG).
If you really need to use gain of 0, try longer exposures (10 to 20 minutes?) to mitigate this read noise problem at gain of 0, especially since you are using a narrow band filter -- although you are probably limited by Bortle 7 skies that prevents you from using very long exposures, even with narrow band filters.
With Bortle 7 skies, you won't really need that much dynamic range for anything but something like M42 and M31. And for those, you can always use high dynamic range techniques (taking images at different exposures). Bortle 2 or 3 skies are different; you have really dark backgrounds, and can make use of the dynamic range.
My recommendation is to bump the gain to 100 to turn on HCG. That uses less time to collect the sub-frames, too.
Personally, I always use gain 100 with my ASI2600 and ASI6200. I usually use 180 second exposures (Bortle 5+ to 6-; different parts of the sky are brighter), but when I use any narrowband filter (Radian Quad for color 2600 and 6200, Chroma 5nm Ha filter for mono 2600), I lengthen the exposures to 300 seconds to mitigate the read noise.
Chen
“Unquote”
I really didn’t think using Gain 0 would be a “Huge” issue using the LExtreme filter
I’ve completed all my procedures listed in previous post so now just waiting for the skies to clear next week
Some very useful information from ZWO and great that you got such a quick response. I was under the impression though from your original post that you had used the same settings with no issues at both of your sites and now you are experiencing the noise issue ?
Some very useful information from ZWO and great that you got such a quick response. I was under the impression though from your original post that you had used the same settings with no issues at both of your sites and now you are experiencing the noise issue ?
Ryan
Yes very surprised about a quick response from ZWO
I’ve mostly used Gain 0 at my Dome under Bortle 3 and have used both Gain 0 and Gain 100 in Sydney under Bortle 7/8
These new generation cameras with the Sony IMX571 sensors or so damn sensitive to changes in LP and sky conditions it’s hard to keep up
I do save my stacks and final images with object name , exposure time , gain setting , location , filters used etc..
Maybe I should go back over my work in the past 18months and create a chart for cross referencing ?
Yes very surprised about a quick response from ZWO
I’ve mostly used Gain 0 at my Dome under Bortle 3 and have used both Gain 0 and Gain 100 in Sydney under Bortle 7/8
These new generation cameras with the Sony IMX571 sensors or so damn sensitive to changes in LP and sky conditions it’s hard to keep up
I do save my stacks and final images with object name , exposure time , gain setting , location , filters used etc..
Maybe I should go back over my work in the past 18months and create a chart for cross referencing ?
Martin
Maybe go back and find one that you did at gain 0 in the same location and see if you had the same noise problem then ? I seem to remember having followed a lot of your work over the years that Gain 0 was what you said you normally used ? It’s certainly all good I for action that you got from ZWO so you can understand why to select certain settings under certain conditions and thanks for sharing it so we can all get an understanding too. I have a feeling your current issue maybe due to something else though ? Maybe ... ?
Ryan,
I hopeful that it’s not the camera’s internal electronics but you never know
Just need some clear nights to do more testing but we are heading into full moon so better in a week or so
Yes Chen from ZWO was really helpful and informative and hope others with the 2600 series cameras can benefit from his comments
Yes very surprised about a quick response from ZWO
I’ve mostly used Gain 0 at my Dome under Bortle 3 and have used both Gain 0 and Gain 100 in Sydney under Bortle 7/8
These new generation cameras with the Sony IMX571 sensors or so damn sensitive to changes in LP and sky conditions it’s hard to keep up
I do save my stacks and final images with object name , exposure time , gain setting , location , filters used etc..
Maybe I should go back over my work in the past 18months and create a chart for cross referencing ?
Martin
I have a 2600MM and 533MM, and have imaged previously on the 533MC (so all based on the same sensor design as the 2600MC.) Personally I've found Gain 100 to be ideal for all of these cameras under all sky conditions for all targets, and I adjust the subexposure time only based on target, sky and filter. Maybe I should try Gain 0 a bit more sometime, but I've never really seen the need as I've never been dissatisified with Gain 100.
I have a 2600MM and 533MM, and have imaged previously on the 533MC (so all based on the same sensor design as the 2600MC.) Personally I've found Gain 100 to be ideal for all of these cameras under all sky conditions for all targets, and I adjust the subexposure time only based on target, sky and filter. Maybe I should try Gain 0 a bit more sometime, but I've never really seen the need as I've never been dissatisified with Gain 100.
I’ve used Gain 0 successfully at my Dome on the South Coast ( Bortle 3 Skies ) pushing 5 min subs and I was aware of all the 2600MC spec charts between Gain 100 and Gain 0 however , I didn’t think the signal loss and noise increase would be so great using Gain 0 under LP Bortle 7/8 skies. The dB figures Chen described are substantial
I’ll be using Gain 100 in Sydney from now on and down at my Dome probably Gain 0 most of the time and Gain 100 depending on sky conditions, moon phase and target type
I know there are some nay-sayers around here, but looking at their published specs gain 100 is a no-brainer.
Imagine the noise as an error bar. The significant reduction in the size of the error bar when the HCG kicks in is enough to push the dynamic range back up to near maximum.
For the same total exposure time, the SNR of the end result will be higher at gain 100 than gain 0.
Well I think I may have discovered the reason for my own noisy images over the last few weeks- I pulled the image train apart last night when that rain started coming through (untouched from the previous night) and what I noticed was there was a distinct layer of dew/fog on my filter inside the filter drawer. It disappeared quickly once I had it all apart but was unmistakeable.
May not be the same for you but thought I’d mention it in case.
Cheers
I suggest you check what others are using for their setting for gain and offsets.
I use a QHY600m and it is not noisy but some settings have lower noise than others and usually optimum for noise control.
I thought others were using a very high number for the gain with that camera.
Greg.
Greg,
When I bought 2600MC in August 2020 I did post on IIS and CN for info on Gain and offset and the majority recommended Gain 100 as this is when the ZWO set the HCG ( high gain mode ) on the Sony IMX 571 where you benefit from the lowest read noise for the highest dynamic range with a well depth of 20K
You tend to forget this and then jump up to Gain 0 with short subs ( 3min ) and expect a nice clean noise free image under heavy B8 LP skies plus throw the moon in for good measure
The ZWO performance charts on both the 2600MC and 2600MM explain it all
ZWO recommend Gain 0 highest dynamic range for dark skies and long subs
I know there are some nay-sayers around here, but looking at their published specs gain 100 is a no-brainer.
Imagine the noise as an error bar. The significant reduction in the size of the error bar when the HCG kicks in is enough to push the dynamic range back up to near maximum.
For the same total exposure time, the SNR of the end result will be higher at gain 100 than gain 0.
Yep the performance charts say it all
I bit of ignorance on my part , you live and learn
Cheers
Well I think I may have discovered the reason for my own noisy images over the last few weeks- I pulled the image train apart last night when that rain started coming through (untouched from the previous night) and what I noticed was there was a distinct layer of dew/fog on my filter inside the filter drawer. It disappeared quickly once I had it all apart but was unmistakeable.
May not be the same for you but thought I’d mention it in case.
Cheers
Thanks Dave
I’m still not totally convinced it’s just a Gain setting but I’ve done everything possible to my camera , cables , scope and software to rule out my checklist items
If I still get noisy images at Gain 100 with short subs ( 1min to 3min ) the cameras going in for service
I just browsed on Astrobin under the 2600MC camera and nearly every image ( Galaxy and Nebula) I looked at from all around the world use Gain 100 and 2 and 3 min subs , broadband and narrowband
They were all excellent images, so clean with plenty of depth and detail
My money is still on what Dave has said. Either fog or dew on some part.
It’s great that you’ve discovered the benifits of gain 100 over gain 0 but just make sure you’re not getting Segwayed away from your original issue. You have said you have used gain 0 for a long time but the noise issue is new. If you are looking on Astrobin and seeing nice clean images on gain 100, make sure you’re also looking at comparable integration times and not comparing a 5hr one night image with a multi night 20hr image. There are many factors as you know that contribute to noise but don’t lose sight of the fact it’s a new issue to you whist using the same settings you have been using.
My money is still on what Dave has said. Either fog or dew on some part.
It’s great that you’ve discovered the benifits of gain 100 over gain 0 but just make sure you’re not getting Segwayed away from your original issue. You have said you have used gain 0 for a long time but the noise issue is new. If you are looking on Astrobin and seeing nice clean images on gain 100, make sure you’re also looking at comparable integration times and not comparing a 5hr one night image with a multi night 20hr image. There are many factors as you know that contribute to noise but don’t lose sight of the fact it’s a new issue to you whist using the same settings you have been using.
Ryan
Ryan,
If you read my last post to Dave , I mentioned “I’m still not totally convinced it’s just a Gain setting”
And yes on Astrobin I was comparing same camera , Gain 100 , same temp -10C , similar subs , similar total integration time , f5 to f7 fl and so on …..
but in saying that I can’t determine the exact bortle scale of their skies as all they mention is imaged from backyard from a particular main town or City
Ongoing cloudy nights is making it hard to do any testing let alone imaging
I’ve serviced my camera
Cleaned sensor
Cleaned protective window
Replaced Desiccant
Bench tested operation and cooling , all ok
Updated all drivers and software
Cleaned my L Extreme filter
A 3 hour window last week enabled me to capture some data on M16 again but this time using Gain 100 Lower read noise ( 1.5 e-rms ) vs Gain 0 ( 3.5 e-rms )
It’s certainly not apples for apples but at least I know Gain 100 under heavy LP skies is the way to go in the future ( no more Gain 0 in Sydney)
Attached labeled images of M16 at Gain 100 and Gain 0
Same target
Similar conditions and moon
Same temp
Same length subs
Dithering
Inclusive of Cal frames ( Flats and Bias )
Same integration time approx 1hr 50 mins
Same DSS Stacking process
Just a quick Autostretch in ST
No real processing
Gain 0 is definitely noisier than Gain 100 especially noticeable in the non nebulosity mid outer regions
Further testing required but I’m confident my camera is Ok and it’s not frost or dew etc…
Bortle 7/8 SQM 18.5 is not exactly ideal for AP and a cooled OSC even with an L Extreme filter can only capture so much signal , the rest is skyglow noise and moon glare noise ….,
have used that almost 99% of the time with the 2600MC
