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Old 17-04-2021, 11:39 AM
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Tinderboxsky (Steve)
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Help with decision; un-cooled vs cooled CMOS camera for EAA

I have been developing some skills and interest in EAA observing using an old Imaging Source DBK41 colour CCD coupled to a Vixen ED103S with focal reducer. The DBK has done well, but I am now thinking of moving up to a more sensitive CMOS camera.

I am using SharpCap to stack and perform basic image enhancements on the fly. I am saving "as viewed" images for observation record purposes only. I am not a fan, nor do I have the time, for post observing image processing. Exposure times range from eight seconds through to one minute single exposures for fainter objects. Total integration times have not exceeded ten minutes.

I live south of Hobart. Evening temperatures during winter will generally range from zero to 5 degrees and Autumn/Spring temperatures seldom are above ten degrees. I don't generally observe in Summer as we don't have dark skies till 11.00 pm due to our long twilight.

So, the big question: is there any advantage to be gained by spending the extra dollars on a cooled camera vs a standard un-cooled one?

I don't think this decision should factor in the possibility of eventually moving to longer exposure imaging.

Any experience feedback or thoughts are most welcome.
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Old 17-04-2021, 11:55 AM
glend (Glen)
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Steve, I chose to buy a ASI294MC (the uncooled version), for my EAA setup. The uncooled version offers some advantages for EAA, like not needing a cooling chip power supply, nor having to worry about the uneven cooling of the chip producing gradients. It offers great sensitivity and well depth, with low noise.
For true EAA use, as an adjunct to visual observation, cooling is simply not needed, as most of your frames or subs will be of very short duration (allowing Sharpcap to align and live stack each one).
The only reason you might want cooling is if you plan to stray into the world of very long sub imaging at some point. Just my opinion.
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Old 17-04-2021, 01:19 PM
Dave882 (David)
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Iíve also had very good success eaa observing and live stacking imaging with the asi294mc uncooled. Iím using an old cpc800 in alt-az with exposures between 5-30sec and over summer in night temperatures up to 28-29degrees. Iíve never had a noise problem so significant that I couldnít see some good detail on the screen within 10min.

I do a bit of post processing on my phone with photoshop express which allows me to pull some further detail from even the feint stuff. But in doing this I start to wrestle with the noise issue which I think can only be properly resolved by going to longer integration times (and for this you need a cooled camera).

For what youíre doing- go for a uncooled.
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Old 17-04-2021, 03:07 PM
ChrisD
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Quote:
Originally Posted by Tinderboxsky View Post
So, the big question: is there any advantage to be gained by spending the extra dollars on a cooled camera vs a standard un-cooled one?
I'm no expert, but this is how I look at this problem.

Reducing the temperature of the sensor will reduce the noise created in the sensor, (Dark Current) but by how much and will you see it?

Well, I've attached the Dark Current v Temperature graph for the ASI294MM pro (the MC should be the same).

The value of dark current (noise) is given in Electrons/second/pixel.
So, by the graph, at 0 degrees you will get about 0.02 e/s/p

So how does that compare to other noise sources?

Well the major source of noise in an image is sky glow.
If you go to:
http://tools.sharpcap.co.uk/
you can enter you camera, scope details, and Bortle value and get the sky glow e/s/p value.

I'm Bortle 5 with a ASI294 and a C8 I get around 0.69 e/s/p from sky glow


So, for me, if the camera was at 0 degrees, I would get 0.71 e/s/p of total noise from the 2 sources (skyglow and dark current) with just 2.8% being from dark current itself.

I don't think cooling would make any difference, the noise from sky glow swamps the noise from the uncooled sensor in most cases.

You probably have better sky than Bortle 5 but you can run the figures now and make your own value judgement.

Chris
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Last edited by ChrisD; 17-04-2021 at 04:45 PM.
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Old 19-04-2021, 10:46 AM
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Tinderboxsky (Steve)
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Thanks for your comments Glen. I followed your EAA equipment thread with interest.

Quote:
Originally Posted by glend View Post
Steve, I chose to buy a ASI294MC (the uncooled version), for my EAA setup. The uncooled version offers some advantages for EAA, like not needing a cooling chip power supply, nor having to worry about the uneven cooling of the chip producing gradients. It offers great sensitivity and well depth, with low noise.
For true EAA use, as an adjunct to visual observation, cooling is simply not needed, as most of your frames or subs will be of very short duration (allowing Sharpcap to align and live stack each one).
The only reason you might want cooling is if you plan to stray into the world of very long sub imaging at some point. Just my opinion.
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Old 19-04-2021, 10:48 AM
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Tinderboxsky (Steve)
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Thanks David. Your experience suggests I will not have a problem with an uncooled camera in the much cooler nights down here.

Quote:
Originally Posted by Dave882 View Post
Iíve also had very good success eaa observing and live stacking imaging with the asi294mc uncooled. Iím using an old cpc800 in alt-az with exposures between 5-30sec and over summer in night temperatures up to 28-29degrees. Iíve never had a noise problem so significant that I couldnít see some good detail on the screen within 10min.

I do a bit of post processing on my phone with photoshop express which allows me to pull some further detail from even the feint stuff. But in doing this I start to wrestle with the noise issue which I think can only be properly resolved by going to longer integration times (and for this you need a cooled camera).

For what youíre doing- go for a uncooled.
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  #7  
Old 19-04-2021, 10:54 AM
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Tinderboxsky (Steve)
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Thanks Chris. I have Bortle 3 to 4 skies and I'll do the analysis for here.



Quote:
Originally Posted by ChrisD View Post
I'm no expert, but this is how I look at this problem.

Reducing the temperature of the sensor will reduce the noise created in the sensor, (Dark Current) but by how much and will you see it?

Well, I've attached the Dark Current v Temperature graph for the ASI294MM pro (the MC should be the same).

The value of dark current (noise) is given in Electrons/second/pixel.
So, by the graph, at 0 degrees you will get about 0.02 e/s/p

So how does that compare to other noise sources?

Well the major source of noise in an image is sky glow.
If you go to:
http://tools.sharpcap.co.uk/
you can enter you camera, scope details, and Bortle value and get the sky glow e/s/p value.

I'm Bortle 5 with a ASI294 and a C8 I get around 0.69 e/s/p from sky glow


So, for me, if the camera was at 0 degrees, I would get 0.71 e/s/p of total noise from the 2 sources (skyglow and dark current) with just 2.8% being from dark current itself.

I don't think cooling would make any difference, the noise from sky glow swamps the noise from the uncooled sensor in most cases.

You probably have better sky than Bortle 5 but you can run the figures now and make your own value judgement.

Chris
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Old 19-04-2021, 10:22 PM
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ChrisV (Chris)
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For the past 4 years I have used an uncooled ASI224MC for live imaging. The subs are so short, so there ain't no time for heat related problems. Anyway, you can dark subtract & use flats in sharpcap live stacking if you want.

Cheers Chris
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Old 20-04-2021, 11:04 AM
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Tinderboxsky (Steve)
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Thanks for your input Chris.


Quote:
Originally Posted by ChrisV View Post
For the past 4 years I have used an uncooled ASI224MC for live imaging. The subs are so short, so there ain't no time for heat related problems. Anyway, you can dark subtract & use flats in sharpcap live stacking if you want.

Cheers Chris
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