Ok, I will admit I have talked about this on other forums but never felt like real logic is applied to the answers, so I I hoping for some real conversation here.
I own an ASI585MC non-cooled camera, this is not my only camera, and yes I own better and cooled cameras.
I have put together a super small portable widefield rig, The goal is to get the whole solution (including portable power and tripod) in a single carry-on
I have accomplished this but due to power and weight needs, I had to stick with the ASI585MC as the camera. I am pretty happy with the field of view, but constantly worry about "how much am I missing out on" by using a non-cooled camera.
More info:
Yes I take calibration frames, and expect to continue to do so.
For this setup my images are limited to no more than 60 seconds, mostly due to guiding, but also hoping to limit heat related noise on the sensor.
The sensor in the ASI585MC seems pretty solid as far as dark/current noise, but it still has some hot pixels and without a cooler the actual temp of the sensor is somewhat variable.
Me talking to myself:
I know the general answer is that (cooled is always better), but in this case it would blow up my whole setup, adding new power requirements, pushing up my weight, and other complications that I am not sure are worth the work.
Banter for the forum
On the newer sony sensors where there is no amp glow and low dark noise, how much difference will a cooled camera make? Really, not in theory.
Will limiting exposure time to 60 seconds help mitigate the lack of a cooled sensor?
Should I still try to run this camera at Unity gain / In HGC mode? or should I dial it down to lower gains hoping to compensate for the lack of a cooled sensor?
Please chime in, but be more thoughtful than (you should just get a cooled camera), Know that I have a asi533mc pro, that could easily be connected to the setup, but this would blow up my power, weight and convenience factors.
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I used and still do use uncooled sensors/cameras (i.e., DSLRs) and thermal noise has never been a really limiting factor thus far (and my "thus far" goes a very long way off…). Yes, cooled sensor are better and even more so at high temperatures but if your sensor temperatures are in the low 30s (Centigrade) and you limit exposures in the minute or so then go for it.
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andrea tasselli:
I used and still do use uncooled sensors/cameras (i.e., DSLRs) and thermal noise has never been a really limiting factor thus far (and my "thus far" goes a very long way off...). Yes, cooled sensor are better and even more so at high temperatures but if your sensor temperatures are in the low 30s (Centigrade) and you limit exposures in the minute or so then go for it. Thanks for the input, even in the summer its not 30 degrees C here in the nights, your comments are making me feel better about this setup.
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I started with a non-cooled 585 and was happy with it until I moved to Oklahoma. On those hot summer nights the noise was just killing me so I bought the cooled version and that's made a huge difference. Noise is much less and of course, the darks are more accurate. In the winter the cameras are almost interchangeable but when it's hot, you'll want the cooled version.
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The dark current doubles every ~7C°. If you go from -20 to +30C° you get over 2 orders of magnitude higher dark current. This doesn't mean the dark current becomes your dominant noise source, but it certainly is a significant increase.
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D. Jung:
The dark current doubles every ~7C°. If you go from -20 to +30C° you get over 2 orders of magnitude higher dark current. This doesn't mean the dark current becomes your dominant noise source, but it certainly is a significant increase. That 7 degree number is great data. Question for you 1. How much of that gets calibrated out with calibration frames? 2. Does that dark current change with exposure times?
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I can't say much about your first question but regarding your second question:
Dark current is measured in e/s/px
For the 585mc, the dark current at
-20C is ~0.001e/s/px
30C is ~0.5e/s/px
Meaning that if you do a 100s exposure at -20C you collected 0.1e as dark current noise per pixel, while at 30C you are at 50e.
The full well of the sensor is 50Ke.
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Clayton Ostler:
Question for you
1. How much of that gets calibrated out with calibration frames?
2. Does that dark current change with exposure times? 1. All of the Dark Current can get calibrated out and most of the noise too, with the right techniques. Your main issue is that you won't know (my guess here) what the actual sensor temperature is so building a pretty large dark library is essential. Dithering helps, if you can. 2. Yes.
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D. Jung:
The full well of the sensor is 50Ke. At zero gain. Elsewhere can be considerably less. IOW, short exposures are essential to keep your effective DR at high temperatures.
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Subtracting a dark frame mitigates the effects of the dark current, but is not a perfect cancellation; it may be good enough though. THe noise that is not there to start with, you don't need to worry about removing afterwards  |
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Thanks to all who have commented. I'm feeling better about this setup. I'm located south of Salt Lake City. Even the warmest nights in the summer are usually 70F degrees by the time it's dark enough to image. And that's only a couple months of the year. (Last night it was 24F)
But even having a set of dark libraries for colder/less cold/medium/warm days would not be that hard to do and is a good idea.
Hearing the others have success without a cooled cam give me hope.
Unfortunately it's about a bottle 6-7 where I usually image so unless I'm going for narrowband, 60 second is kind of the sweet spot for the sky, the camera and the mount.
The suggestion of dithering is much appreciated and I would not have thought of that on my own.
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You can go lower with your subs using this sensor. I shoot under bortle 7-8. I haven't tried broadband but with a 6nm dual band filter, my standard sub ex. time is 15 sec. with a gain of 255 (HCG mode).
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D. Jung:
I can't say much about your first question but regarding your second question:
Dark current is measured in e/s/px
For the 585mc, the dark current at
-20C is ~0.001e/s/px
30C is ~0.5e/s/px
Meaning that if you do a 100s exposure at -20C you collected 0.1e as dark current noise per pixel, while at 30C you are at 50e.
The full well of the sensor is 50Ke. I have been thinking a bit more about my answer here and I think it does not fully capture the actual problem. - The dark current itself is not the problem and is not noise if it is constant, i.e. having a variance σ^2 of 0. Then it would just be an offset which could be removable by simple subtraction.
- The dark current varies between pixels and these variations increase with temperature, such that the variance σ2 increase with temperature with some function σ^2(t).
- So if we subtract a dark frame from our light frame, we remove the offset, but the variance of the dark current embedded into the light frame remains. even worse, since the dark frame itself is noisy, we actually increase the noise of the light frame by said subtraction. in the case of identical variance σ^2 of the dark and light frame, the noise, i.e. the standard deviation would increase by sqrt(2σ^2) = 1.414. even if the variance of the dark frame was 0 we would still be left with the original variance in the light frame after subtraction!
- If we assume the dark current to follow a poison distribution the standard deviation σ is the sqrt of the amplitude. And for above dark current example would yield for -20C a σ=sqrt(0.001) and for the 30C case σ=sqrt(0.5), i.e. a noise increase of factor of 22.
That is my feable attempt at statistical math (likely wrong) reminding me of this one below  |
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Cooled cameras ease of use when it comes to darks and biases should not be under estimated.
Makes every session smoother
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D. Jung:
D. Jung:
I can't say much about your first question but regarding your second question:
Dark current is measured in e/s/px
For the 585mc, the dark current at
-20C is ~0.001e/s/px
30C is ~0.5e/s/px
Meaning that if you do a 100s exposure at -20C you collected 0.1e as dark current noise per pixel, while at 30C you are at 50e.
The full well of the sensor is 50Ke.
I have been thinking a bit more about my answer here and I think it does not fully capture the actual problem.
- The dark current itself is not the problem and is not noise if it is constant, i.e. having a variance σ^2 of 0. Then it would just be an offset which could be removable by simple subtraction.
- The dark current varies between pixels and these variations increase with temperature, such that the variance σ2 increase with temperature with some function σ^2(t).
- So if we subtract a dark frame from our light frame, we remove the offset, but the variance of the dark current embedded into the light frame remains. even worse, since the dark frame itself is noisy, we actually increase the noise of the light frame by said subtraction. in the case of identical variance σ^2 of the dark and light frame, the noise, i.e. the standard deviation would increase by sqrt(2σ^2) = 1.414. even if the variance of the dark frame was 0 we would still be left with the original variance in the light frame after subtraction!
- If we assume the dark current to follow a poison distribution the standard deviation σ is the sqrt of the amplitude. And for above dark current example would yield for -20C a σ=sqrt(0.001) and for the 30C case σ=sqrt(0.5), i.e. a noise increase of factor of 22.
That is my feable attempt at statistical math (likely wrong) reminding me of this one below
I bet we can find astrophotographers in the same boat, ahahaha. This makes me want to run an experiment with non-cooled. Wonder if I just skipped darks and bias entirely, just did my flats for dust and light path stuff, and hoped Blurxterminator is smarter than the "guessing" calibration frames. Will try sometime soon
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Clayton Ostler:
D. Jung:
D. Jung:
I can't say much about your first question but regarding your second question:
Dark current is measured in e/s/px
For the 585mc, the dark current at
-20C is ~0.001e/s/px
30C is ~0.5e/s/px
Meaning that if you do a 100s exposure at -20C you collected 0.1e as dark current noise per pixel, while at 30C you are at 50e.
The full well of the sensor is 50Ke.
I have been thinking a bit more about my answer here and I think it does not fully capture the actual problem.
- The dark current itself is not the problem and is not noise if it is constant, i.e. having a variance σ^2 of 0. Then it would just be an offset which could be removable by simple subtraction.
- The dark current varies between pixels and these variations increase with temperature, such that the variance σ2 increase with temperature with some function σ^2(t).
- So if we subtract a dark frame from our light frame, we remove the offset, but the variance of the dark current embedded into the light frame remains. even worse, since the dark frame itself is noisy, we actually increase the noise of the light frame by said subtraction. in the case of identical variance σ^2 of the dark and light frame, the noise, i.e. the standard deviation would increase by sqrt(2σ^2) = 1.414. even if the variance of the dark frame was 0 we would still be left with the original variance in the light frame after subtraction!
- If we assume the dark current to follow a poison distribution the standard deviation σ is the sqrt of the amplitude. And for above dark current example would yield for -20C a σ=sqrt(0.001) and for the 30C case σ=sqrt(0.5), i.e. a noise increase of factor of 22.
That is my feable attempt at statistical math (likely wrong) reminding me of this one below
I bet we can find astrophotographers in the same boat, ahahaha.
This makes me want to run an experiment with non-cooled. Wonder if I just skipped darks and bias entirely, just did my flats for dust and light path stuff, and hoped Blurxterminator is smarter than the "guessing" calibration frames. Will try sometime soon On my cooled 585 I find that darks really aren't needed. You can do perfectly well with just flats and bias frames.
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There's a lot of response on the survey showing there are individuals that can prove the cooled is kicking out better images. Id love to see side by side stacked and calibrated images with say 1 hr of data between a cooled and non cooled 585.
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I can do that at my next imaging session but I don't think it will show you much at this time of year. It would be much more informative to do it sometime in July.
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Guess I'm just gonna stir the pot by posting this but I've discovered the 585MC does actually have amp glow. It gets particularly bad once the sensor reaches 30C. It does calibrate out however with darks.
The 585MC Pro does still exhibit slight traces of it, but it hasn't bothered me enough to shoot darks.
I have and use both version of the camera. If you have specific questions, let me know. Short answer is the cooled is superior, however if you live in a cold climate, you could easily get away with the uncooled.
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Clayton Ostler:
Ok, I will admit I have talked about this on other forums but never felt like real logic is applied to the answers, so I I hoping for some real conversation here.
I own an ASI585MC non-cooled camera, this is not my only camera, and yes I own better and cooled cameras.
I have put together a super small portable widefield rig, The goal is to get the whole solution (including portable power and tripod) in a single carry-on
I have accomplished this but due to power and weight needs, I had to stick with the ASI585MC as the camera. I am pretty happy with the field of view, but constantly worry about "how much am I missing out on" by using a non-cooled camera.
More info:
Yes I take calibration frames, and expect to continue to do so.
For this setup my images are limited to no more than 60 seconds, mostly due to guiding, but also hoping to limit heat related noise on the sensor.
The sensor in the ASI585MC seems pretty solid as far as dark/current noise, but it still has some hot pixels and without a cooler the actual temp of the sensor is somewhat variable.
Me talking to myself:
I know the general answer is that (cooled is always better), but in this case it would blow up my whole setup, adding new power requirements, pushing up my weight, and other complications that I am not sure are worth the work.
Banter for the forum
On the newer sony sensors where there is no amp glow and low dark noise, how much difference will a cooled camera make? Really, not in theory.
Will limiting exposure time to 60 seconds help mitigate the lack of a cooled sensor?
Should I still try to run this camera at Unity gain / In HGC mode? or should I dial it down to lower gains hoping to compensate for the lack of a cooled sensor?
Please chime in, but be more thoughtful than (you should just get a cooled camera), Know that I have a asi533mc pro, that could easily be connected to the setup, but this would blow up my power, weight and convenience factors. The advantage to non-cooled is spending less money.
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BryanHudson:
Clayton Ostler:
Ok, I will admit I have talked about this on other forums but never felt like real logic is applied to the answers, so I I hoping for some real conversation here.
I own an ASI585MC non-cooled camera, this is not my only camera, and yes I own better and cooled cameras.
I have put together a super small portable widefield rig, The goal is to get the whole solution (including portable power and tripod) in a single carry-on
I have accomplished this but due to power and weight needs, I had to stick with the ASI585MC as the camera. I am pretty happy with the field of view, but constantly worry about "how much am I missing out on" by using a non-cooled camera.
More info:
Yes I take calibration frames, and expect to continue to do so.
For this setup my images are limited to no more than 60 seconds, mostly due to guiding, but also hoping to limit heat related noise on the sensor.
The sensor in the ASI585MC seems pretty solid as far as dark/current noise, but it still has some hot pixels and without a cooler the actual temp of the sensor is somewhat variable.
Me talking to myself:
I know the general answer is that (cooled is always better), but in this case it would blow up my whole setup, adding new power requirements, pushing up my weight, and other complications that I am not sure are worth the work.
Banter for the forum
On the newer sony sensors where there is no amp glow and low dark noise, how much difference will a cooled camera make? Really, not in theory.
Will limiting exposure time to 60 seconds help mitigate the lack of a cooled sensor?
Should I still try to run this camera at Unity gain / In HGC mode? or should I dial it down to lower gains hoping to compensate for the lack of a cooled sensor?
Please chime in, but be more thoughtful than (you should just get a cooled camera), Know that I have a asi533mc pro, that could easily be connected to the setup, but this would blow up my power, weight and convenience factors.
The advantage to non-cooled is spending less money. And less power to run and less weight (although that very small). I'm still kind of on the fence about the whole thing.
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I own both the cooled and uncooled versions and the bottom line is, in cold temps there really isn't much difference. On hot summer nights there is a huge difference with the uncooled version being almost unusable.
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The uncooled version can be bought by R$ 2999 here in Brazil, while the cooled one costs R$ 4799, 60% more. That cheap TEC cooler for phones that I'm using cools down the camera from 30 to about 20 C, and costs about R$ 150. From 30 to 20 C the dark current is reduced from 0.5 to 0.125. With a larger 30W cooler I was able to cool it down to 8 C, which gives a dark current of about 0.017 e/s/pix.
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Tony Gondola:
I own both the cooled and uncooled versions and the bottom line is, in cold temps there really isn't much difference. On hot summer nights there is a huge difference with the uncooled version being almost unusable. Good to know. When you say unusable, have you found a sweet spot on max exposure time that will work? Would 60 or even 30 second exposures work?
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