NGC253 - 60 min subs-reprocessed detail with colour
Not sure where to place this - here or in the equipment section but since there is an image, here will do.
At Astrofest I was doing the usual 10 min subs with somewhat crappy seeing using OAG guiding through the QSI583WSG using the ZWO ASI120MM camera and getting round stars, so I began to wounder what was the limit I could go using an EQ6 mount.
I started doing 30 minute subs and finally went to 1 hour or 3600 sec subs an NGC253. I managed to get 2x3600 sec subs, 4x1800 sec subs and 5x10 min subs along with my RGB data.
I have attached one of the 3600 subs which had a little touch up in PS3 but the data didn't need much pushing as it was so easy to work.
Ill let this image speak for itself but I still haven't answered the question as to how long my EQ6 can track for.
What has amazed me is that there are more small galaxies in the background of the image that there are stars. I spent ages just going through the inverted image.
Allan
REPROCESSED DATA
Ive reprocessed all my data with a combination of Pixinsight as well as PS3 and added the colour data that I accumulated during that session. The colour data consisted of 5x10min RGB subs which was added to the luminance data. According to Pixinsight the data that it threw up while processing indicated that the 10 min subs had a noise factor of 4x that of the 3600 sec subs.
What Im very happy with is that in the luminance data the streamers, which come out of the plane of the galaxy, are just being recorded at the edge of the core and are plainly seen. Ive only ever seen this in images from my 10" SCT and surprised that it can be seen with a 5" refractor.
I must admit that I got lost in the Pixinsight processing and at times didnt know where I was and so had to finish it off with PS3.
Hope you like the final rendition and comments welcomed.
Allan
Last edited by allan gould; 19-08-2013 at 11:22 PM.
Great tracking. 60 minutes is impressive but the obvious downside to super long exposures is clouds wrecking a run and wasting such a large amount of imaging time.
With an OAG and accurate polar alognment to prevent field rotation there should not be a mechanical limit to the length of the exposure. The limit will be noise and wasted time with cosmic rays, planes, satellites etc.
I never bother going over 10 mins for these reasons. The amount of signal is the same with 6 x 600 sec exposures vs 3600 sec but the noise will be different depending on lots of different factors.
An interesting experiment to try though.
Dont know why all my posts from the last few days have been deleted, must have upset the IIS gods or something.
Thanks for all your comments as they are really appreciated and I did respond to you all individually.
I did post a thread of the colourised version here in the deep sky section but that has been deleted - dont know why? The data was very easy to process as it contained several one hour subs and a set of 30 min and 10 min subs.
Far less noise that a bunch of 5 or 10 min subs and very easy to work with.
Allan
Dont know why all my posts from the last few days have been deleted, must have upset the IIS gods or something.
Thanks for all your comments as they are really appreciated and I did respond to you all individually.
I did post a thread of the colourised version here in the deep sky section but that has been deleted - dont know why? The data was very easy to process as it contained several one hour subs and a set of 30 min and 10 min subs.
Far less noise that a bunch of 5 or 10 min subs and very easy to work with.
Allan
You probably know this, but the crash at IIS destroyed all posts from Wednesday on! Nothing personal...there just wasn't a backup for the lost hard drive. (so I read elsewhere on this site in the general comments section)
BTW, wonderful shot. Very impressive effort in guiding and not for the faint of heart!
Peter
You probably know this, but the crash at IIS destroyed all posts from Wednesday on! Nothing personal...there just wasn't a backup for the lost hard drive. (so I read elsewhere on this site in the general comments section)
BTW, wonderful shot. Very impressive effort in guiding and not for the faint of heart!
Peter
Thanks Peter. ATM Im reprocessing all of my images using PixInsight as it makes a huge difference to the final image and that will take me some time.
I read recently that noise will be greater with a very long exposure than a shorter one. Not sure why, but perhaps some property of CCDs.
Did you notice that it had more noise than a shorter one at the same temperature?
I would have though the main issue with super long exposures apart from practical considerations of lost time if clouds come over, would be overfilling the wells and getting blown highlights. I suppose it would depend on what you were imaging. M42 or M8 would not be well suited to that strategy but a dim galaxy may well be.
Greg
I was imaging at -30C with the 8300 chip in the QSI and like you mentioned I thought that the center of the galaxy would be blown out. But when I looked at the histogram of 10 and 30 min subs it was nowhere near saturating. Obviously some stars which are blown at 10 min will be, but not as many as you would think. Anyway in relation to noise I must say that the background was virtually noise free at 60 min exposure and very very easy to process. At the moment I'm going to reprocess this image in pixinsight as I've just started using it and I find in many respects it gives a better image than I can get in PS. When I've done it I will post it here. I will post both 10 and the 60 min subs as a comparison.
Allan
From Terry B
"With an OAG and accurate polar alignment to prevent field rotation there should not be a mechanical limit to the length of the exposure."
I agree, but I must add the following:
the lubrication of Allan's NEQ6 is very very good ! With 60 mins some drift could happens because of mechanical effort.
I have a NEQ6, and I had to do maintenance just because of it.
And it is very impressive that no significant saturation occurred.
oh that colour version - covet thy neighbours photons - thats a gorgeous shot in the colour repro Alan
I was lucky to get so many with you and the 11" and hyperstar gobbling down everything on the field, but what a great 10 nights!
Glad you liked the colour repro.
Allan
Where's the high-res?
