ngc6888 - last night...

[JohnP]

another late one last night....

did ngc6888 through zs66 - 20X5min subs with ha filter..

Ta,  John

[Mike]

Oooh the Crescent. That is a nice one in colour. Good image John.

[JohnP]

Cheers Mike - It's tough doing rgb though when you only have about 2hrs of dark skies. I want to try this object again as I am still struggling with long exposure guiding.. I am sure I can get a lot more out of it if I could do 10min subs...

John

[Mike]

Yes it's surface brightness isn't great. This is the time of the year when you want a nice cooled one shot colour CCD.

[Fay]

Very nice image, John. Even twice as nice with 10 min subs.

[MarkS]

What an interesting object.  Nice one ...

[JohnP]

Thks Fay & Mark. Yep Mark it has loads going on it sits in a massive field of nebulosity - hints of which are just starting to show in mine. This is one of my favourite objects & I will try again. The image is a bit fuzzy as I have the same issue as you do i.e. drifting between subs.. Needs 10min subs to do justice.

John

[Rocket Pooch]

was that a hint?

[Rocket Pooch]

This would have been ok if the camera did not have loads of hot pixels and thermal instability, its going back.

[Fay]

Chris, that image could have knocked me off my chair. Do you think you have a dodgy camera, hope it is not common to all of them. Be interesting to see what happens, & to see it taken with another Atik 314L. 

[Rocket Pooch]

Yes I'm not happy with it, the camera should be stable and have few is any hot pixels, have a look in the middle of the image you will see the star trails caused by guiding errors.

This was a stack of 11 10 minute subs, I also have 6 10 minute O3's to add for a false colour image, but I might not post it becase of the hot pixels.


Chris

[Mike]

It is a nice image and your focus is spot on. But those hot pixels sure do ruin it. After paying all that money then it definitely needs to go back.

[MarkS]

Chris,

You could improve the image by performing a sigma stack - that should remove most of the hot pixels.  I always have to do that as part of my Canon processing sequence to get rid of residual pixel problems after subtracting darks. 

Whether or not the sensor is outside its advertised tolerance is a matter for you to resolve with the supplier.  Maybe you should create a dark to identify the number of affected pixels.

Mark

I forgot to say that in spite of the hotties, it really is a beautiful image.

[Mike]

It does seem to have a rather large number of hot pixels. I think I would send it back if it were mine.

[Rocket Pooch]

Hi,

Ok reprocessed and it looks ok, but I don't think the cooling is great.



False colour version will be on the way.

[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.