ngc6888 - last night...

[RobertM]

That looks really very good now Chris.

Why don't you think the cooling is working properly ?  I can't see anything from the image that would lead me to that conclusion.

[Fay]

I think the same as Robert, very nice, but what is there about it that makes you think cooling is not all that?

[MarkS]

Chris,

It's easy to investigate your thermal noise and it can be done on a cloudy night.

Generate 2 darks for each of the following exposures whilst keeping temperature more or less constant:
1 min, 5 min, 10 min, 15 min, 20 min

Difference the two 1 min exposures and calculate the standard deviation of the difference frame.
Do the same for the other exposure lengths.

You now have a table of s.d. versus exposure length.
From this table you can draw a graph and calculate:
1) Gain (electrons/ADU)
2) Read noise (electrons) at this temperature
3) Dark current (electrons/sec) at this temperature

I'll dig out the exact details on how to derive this info from the graph.

I did this for my Canon both at room temperature and then again at fridge temperature.

Mark

[RobertM]

Hi Mark, that's very interesting and it would be useful to have that information.

Did you see that some guy in Australia modded a fridge to put his SLR in ! It was a small fridge but even so I think thats taking things a bit far ... and looks a bit odd stuck on the end of the telescope - can't remember whether the fridge was mounted on the telescope or the other way around - made me laugh anyway.

[The Thing]

Hi Mark, yes I agree that is very interesting, I wondered if I could find a use for a little 12v plastic beer fridge. My Minolta DSLR is very noisy unless its a nice cold night. I am in awe at some of the picture you guys produce. I have only been successful with planets to date.