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I’ve had mine for less than a year and stick to Unity gain and -5 (-10 in summer months). I usually make subs of 180s of 120s. I’m sure it could be tweaked more but I’d rather spend time on something else.
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There is a reasonable rule of thumb for the temperature setting. Beyond some point a lower temperature will not significantly decrease your noise and running too low is a stress on the fan and potential condensation, so you don't really want to run lower than you need to. And most coolers will only get you about 30C below ambient anyway.
So the rule of thumb is simply that you don't want the dark noise due to dark current to contribute significantly to the read noise. So in your subexposure with this camera at 120 gain say, you are something like 2.1 e read noise. The corresponding dark noise will depend on the sub exposure time. For example, say you do 100 seconds subs. The dark current for this camera at 0C would be 100*0.0070= 0.7 e. Now the dark current average signal gets subtracted out when you do the dark at the same conditions, this is important, so the dark signal isn't in your image. But it does add noise, the sqrt (0.7) = 0.84 e. Read noise for the sub is 2.1. Total noise is calculated in quadrature since they are random and indepedent, so with dark noise added it is sqrt(2.1^2 + 0.84^2) =2.26 e. The contribution of the dark noise to the total noise to that sub is only 0.16 e/2.26 e = 7%! So zero degrees is fine for up to about a 100 second exposure or so. For a longer exposure you will want to go to lower temperature if you can, easy to calculate where you want to be for any particular sub length using this same procedure.
Now if your skies are heavily light polluted, the sky background noise is likely to be your limiting noise, the read noise can be much less than the background noise. Also, your exposure times will be limited. So with LP you may not have to cool as much as if you are in dark site where you want really long subs.
Hope this helps
Rick
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Rick Veregin:
There is a reasonable rule of thumb for the temperature setting. Beyond some point a lower temperature will not significantly decrease your noise and running too low is a stress on the fan and potential condensation, so you don't really want to run lower than you need to. And most coolers will only get you about 30C below ambient anyway.
So the rule of thumb is simply that you don't want the dark noise due to dark current to contribute significantly to the read noise. So in your subexposure with this camera at 120 gain say, you are something like 2.1 e read noise. The corresponding dark noise will depend on the sub exposure time. For example, say you do 100 seconds subs. The dark current for this camera at 0C would be 100*0.0070= 0.7 e. Now the dark current average signal gets subtracted out when you do the dark at the same conditions, this is important, so the dark signal isn't in your image. But it does add noise, the sqrt (0.7) = 0.84 e. Read noise for the sub is 2.1. Total noise is calculated in quadrature since they are random and indepedent, so with dark noise added it is sqrt(2.1^2 + 0.84^2) =2.26 e. The contribution of the dark noise to the total noise to that sub is only 0.16 e/2.26 e = 7%! So zero degrees is fine for up to about a 100 second exposure or so. For a longer exposure you will want to go to lower temperature if you can, easy to calculate where you want to be for any particular sub length using this same procedure.
Now if your skies are heavily light polluted, the sky background noise is likely to be your limiting noise, the read noise can be much less than the background noise. Also, your exposure times will be limited. So with LP you may not have to cool as much as if you are in dark site where you want really long subs.
Hope this helps
Rick
*** Thank you for this Rick. Lots of information to take in but I will try process it***
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I have the QHY version and it's gain 10 offset 30 for that one. It's pretty much the ZWO gain 111. I also use -10C.
Just for the record, this camera is a bit aged. Compared to the new cameras it's a lot noisier and there is that amp glow to deal with.
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I have the QHY version and it's gain 10 offset 30 for that one. It's pretty much the ZWO gain 111. I also use -10C.
Just for the record, this camera is a bit aged. Compared to the new cameras it's a lot noisier and there is that amp glow to deal with.
*** Yeah the darks deals with that amp glow***
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Abdul Thomas Jnr:
I have the QHY version and it's gain 10 offset 30 for that one. It's pretty much the ZWO gain 111. I also use -10C.
Just for the record, this camera is a bit aged. Compared to the new cameras it's a lot noisier and there is that amp glow to deal with.
*** Yeah the darks deals with that amp glow*dark frames eliminate the amp glow |
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colour = 100
dual band / narrow band filter = 300
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I heard something about using dark flats instead of bias frames for that particular model as stacking is worse with bias frames. Anyone concur?
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I always use dark flats so haven't tried bias
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Very good cooler on this camera.
Gain 111 /offset 10 /-15°C (works even at 25°C outdoor temp)
120s on it/uv cut and 300s on duo band ZWO.
The amp glow is easy to remove.
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Gain is a trade-off of read noise vs dynamic range.
I'm in a Bortle 7 zone, so for broadband I need all the dynamic range I can get with the LP raising the background so much and the read noise will disappear in the shot noise anyway (uncorrelated noise adds in quadrature). That's why I use gain 54 for broadband. I tried gain 0 but the banding is horrible and didn't calibrate out.
For narrowband the shot noise from LP is much less (which is good, but there's less place to hide the read noise) and also I no longer suffer all that LP gobbling up dynamic range. That's why I shoot narrowband at gain 111 (unity) - not that there is anything special with that, this sensor does not have a HCG mode, but it's a nice middle ground.
As far as temperature goes I shoot at -15C but -10C would be fine too, it's just where I started with this camera when I shot my dark lib and I've not bothered deviating from that since. Where I live, -15C is doable year-round at night. As long as that's the case anything around or below freezing (0C) is just fine. It's more about keeping a stable temperature from that point on.
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Benny Colyn:
Gain is a trade-off of read noise vs dynamic range.
I'm in a Bortle 7 zone, so for broadband I need all the dynamic range I can get with the LP raising the background so much and the read noise will disappear in the shot noise anyway (uncorrelated noise adds in quadrature). That's why I use gain 54 for broadband. I tried gain 0 but the banding is horrible and didn't calibrate out.
For narrowband the shot noise from LP is much less (which is good, but there's less place to hide the read noise) and also I no longer suffer all that LP gobbling up dynamic range. That's why I shoot narrowband at gain 111 (unity) - not that there is anything special with that, this sensor does not have a HCG mode, but it's a nice middle ground.
As far as temperature goes I shoot at -15C but -10C would be fine too, it's just where I started with this camera when I shot my dark lib and I've not bothered deviating from that since. Where I live, -15C is doable year-round at night. As long as that's the case anything around or below freezing (0C) is just fine. It's more about keeping a stable temperature from that point on.
*** I normally shoot at gain 53 for broadband but im going to try gain 111 for all like most people suggests and see what's best***
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Mark McKenzie:
I heard something about using dark flats instead of bias frames for that particular model as stacking is worse with bias frames. Anyone concur?
Use dark flats, many CMOS cameras have a weird response at the minimum exposure. In any event, best to always use darks not bias, especially if the camera is relatively noisy. How can one expect to remove dark noise without running darks? Darks contain the bias, so no need to run bias as well.
Rick
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