Thermal shock & inner condensation, cooled cameras

The camera software will apply an appropriate ramp in cooling down. Don't worry about the warming up (I normally switch the thing off once I'm finished with the session). My advice is to cool down to -10 and see how it goes before going any further down. If all is well take the temperature down and if no frosting appears than you'll be alright.

Hello Gabriel,

I usually have a 5 min ramp to cool and to warm the camera. But let me challenge you in one thing: maybe you don't need to cool to negative temperatures, as thermal noise of that camera is quite low. As far as I can see in the website, the thermal noise is as follows:

T (ºC)     DarkCurrent (e/s)    ThermalNoise (e (300sec))
0                    0.00195                               0.765
-10                0.00050                                0.387
-15                0.00025                                0.274

In the last column, you have the thermal noise of a 300 sec exposure.

Depending on the sky you shoot, your shot noise for the same 300 sec exposures (considering a color camera and an F5 telescope) should be:

Bortle                 SkyBack (e/s)                 SkyBack (e (300sec))                 ShotNoise (e )
2                                0.30                                              90                                    9.49
4                                0.57                                             171                                 13.08
6                                3.97                                           1191                                 34.51
8                                8.30                                           2490                                 49.90

Since you add noises using the quadrature rule, and considering the worst case (0ºC), the combined noise is as follows:

Bortle                 ShotNoise (e )               Total Noise (e )
2                                    9.49                             9.52
4                                  13.08                           13.10
6                                  34.51                           34.52
8                                  49.90                           49.90

So, you should be fine shooting at 0º or even a bit higher as it barely contributes to the noise and has several advantages such as less stress on the sensor and lower power consumption.

Just a thought… 

Note: I have assumed an OSC camera with clear filter. Final conclusion may vary according to filters used or mono/OSC.

Cheers,
André

Arun H:
Hi Andre -

To be accurate - your numbers are not thermal noise but actual dark current. The noise from this dark current will be the square root of these numbers (from the Poisson distribution).

Hi Arun,

That is correct and thanks for bringing it up - post is now revised. Despite forgetting to take the square root for thermal noise, final conclusion still holds.

Cheers.

Arun H:
Andre-

yes, this is the way to look at it. I made a similar point in a different thread. Once your shot noise from sky becomes dominant, there is no benefit from cooling further. Do note that the sky background will be significantly less than your numbers if you are doing narrow band and there, there is probably some benefit to going deeper in terms of cooling.

Yes, correct. In this case I assumed it was an OSC with a clear filter, since it is the first astrocamera of Gabriel. Of course there are several assumptions here, like the f-ratio of telescope and the use of a clear filter (if any), and conclusion may vary according to those conditions.

Andre Vilhena:
Hello Gabriel,

I usually have a 5 min ramp to cool and to warm the camera. But let me challenge you in one thing: maybe you don't need to cool to negative temperatures, as thermal noise of that camera is quite low. As far as I can see in the website, the thermal noise is as follows:

T (ºC)     DarkCurrent (e/s)    ThermalNoise (e (300sec))
0                    0.00195                               0.765
-10                0.00050                                0.387
-15                0.00025                                0.274

In the last column, you have the thermal noise of a 300 sec exposure.

Depending on the sky you shoot, your shot noise for the same 300 sec exposures (considering a color camera and an F5 telescope) should be:

Bortle                 SkyBack (e/s)                 SkyBack (e (300sec))                 ShotNoise (e )
2                                0.30                                              90                                    9.49
4                                0.57                                             171                                 13.08
6                                3.97                                           1191                                 34.51
8                                8.30                                           2490                                 49.90

Since you add noises using the quadrature rule, and considering the worst case (0ºC), the combined noise is as follows:

Bortle                 ShotNoise (e )               Total Noise (e )
2                                    9.49                             9.52
4                                  13.08                           13.10
6                                  34.51                           34.52
8                                  49.90                           49.90

So, you should be fine shooting at 0º or even a bit higher as it barely contributes to the noise and has several advantages such as less stress on the sensor and lower power consumption.

Just a thought... 

Note: I have assumed an OSC camera with clear filter. Final conclusion may vary according to filters used or mono/OSC.

Cheers,
André

*Hello Andre, thank you so much for the information above. That is certainly a good point & something I will be implementing into my imaging. Everyone here is above & beyond, thank you for the help 

Gabriel

I would agree fully with @JohnAdastra as I have the 071 as well as the 294. I have found that the 294 is more subject to this than the 071 however. I used to go to -15 but because of the summer months here in Michigan I found that I can’t get to it easily so I have shot at -5 year round without an issue and I’ve been happy with the results.

I also agree with @andrea tasselli in that most software seem to have the ramp up/down controlled in the software. At least it seems like it in SharpCap Pro.

Congrats on the new 533 btw! You’ll enjoy it for sure!

Dale