Cocoon Nebula 25-6-12

[Carole]

Done in the early hours this morning.
An experiment using 600sec subs and lowering the ISO to 400.
Modified Canon 450D and CLS Filter
Skywatcher ED120 Pro
Guided with PHD and QHY5
Captured in APT with dithering on NEQ6
New Bias frames taken as previous ones were a year old and needed ones for 400ISO anyway.

16 x 600secs
there is still noise (it was 16 degrees), but I think less than there would have been at 800 ISO.
I might do this again another evening using 300sec subs and 800 ISO to compare.

Link to larger file:
http://gallery.orpington-astronomy.org.uk/albums/userpics/10047/Coccon_Nebula_24-6-12_400ISO_x_600secs.png

[RobertM]

Hi Carole,

I think that's a really good result for a DSLR from Bromley.  You're really getting limited by where you are now with that Camera because you can't cut out all the light pollution.  The focus looks spot on across the frame so really it's only signal that's limiting the image... More subs I'm afraid...

I also think you should try to find some other noise reduction methods that might help out.

Robert

[Carole]

Thank you Robert, not having done this one before I was not sure what to expect.

I also think you should try to find some other noise reduction methods that might help out.

Yes I am trying, that's the reason why I did the above experiment i.e. lengthen subs but reduce ISO.

Obviously more subs as you say, clouds permitting.

Carole

[MarkS]

That's a surprisingly good result from Bromley - you've even got the dust lane beginning to appear.

Focus is good, colours are good and the stars have good colour.  Unfortunately the Canon banding problem is noticeable  - more obvious in the dust lane.

On a technical point, even with a CLS filter the sky background will be the limiting factor so there's really no need to use longer subs.  Longer subs will only make a difference when the sky background and thermal noise are so low (compared to the read noise) that you need to increase the exposure to drown out the read noise.

Mark

[Carole]

Thanks Mark.

Unfortunately the Canon banding problem is noticeable

Do you know, I hadn't even noticed that this time, but you're right.

there's really no need to use longer subs etc etc

As I said it was just an experiment, I am hoping to go back to the same image again and do it all again using the normal 800 ISO and 300 sec subs from the same site and compare them. 

Carole

[JohnP]

Thats quite nice Carole from Brombles... I'm impressed - John

[Fay]

A good image Carole

[Carole]

Thank you John and Fay. 

I'm getting a long list of images that need doing from a dark site, but at least if I can do them from home first it gives me some insight into what is needed.

Carole