Spent last night fitting & adjusting my new OAG. As a quick test when finished thought I would take a sequence of images of m57 using 5min, 10min, 20min & 30min sub to see if it is possible to get outer halo from Light Polluted Bromley. Anyway result shown below - just a simple stretch of raws in aip4win... Image acquired using ED80 + Atik16ic with Baader 7nm Ha filter.
As you can see it is just visible on 20 & 30min subs... Blimey don't think I'm going to bother with this...!
Cheers, John.
(http://www.jpastronomy.co.uk/graphics/web/SingleSubTest.jpg)
It will become visible on shorter subs that are stacked. Just need lots. I'd go for it John. Looks promising.
That's a good comparison John, though to me it looks like it is possible (just) - the question is whether anyone has the patience to get enough subs to make a good image.
btw, what was the calibrated background counts for each image?
Robert
Quote from: RobertM
btw, what was the calibrated background counts for each image?
And what is the background count in electrons?
Thks.
Statistics 5min Sub (Whole image) is - Min 269, Max 48844, Median 395
Statistic 30min Sub (Whole image) is - Min 699, Max 48605, Median 916
These numbers are straight from raws (uncalibrated)
(No idea why 5min sub has a higher Max than 30min sub....)
Avg background value for darks is approx 300..
Below is quick, cropped, uncalibrated stack of the 5 images I took (1x5min, 1x10min, 2x20min & 1x30min) - Halo def showing but you have to stretch image so far for it to show... :-( Not a lot for 85mins...!
The 7nm Baader is a very narrow band filter (maybe too narrow for me..) I may try again using my 12nm Ha filter..
(http://www.jpastronomy.co.uk/graphics/web/stacktest.jpg)
Well you got it!
Nice thought though trying to get that, what you need is a faster scope with more focal legth to get you in there! ;)
ummm.... a 200mm f4 would do nicely Mr. Suddell.... ;) Darker skies would be good as well.
Sensitive camera, fast scope and dark skies ... sound's like you're ready for a DSC ?
Your background counts are interesting...
A median of 916 is very low for 30 mins around the Bromley area. I did some 7nm Ha subs of this a few days ago but I don't think even the calibrated subs had background counts that low. I'd better check the filters are the right way round !
I would say the 13nm will give a worse background count and mask more faint image detail, that's the advantage of the 7nm. I would say 3nm would be of even more benefit (if they weren't so pricey that is).
Robert
I did 5x1800 on it last night, Atik & SW 120. Could not see that much of the outer halo. Used 12nm ha filter.
I think life may be too short!
Just had a play with the 85mins of data that I took a week or so ago. Really tough to process - this is about best I could do. I have enlarged X200% (so same soft issues as Carole had with hers due to resampling). As you can see no hint of ring showing - it is so dim that any chance to show it just blows out m57...
John.
(http://www.jpastronomy.co.uk/graphics/web/m57_processedX2.jpg)
Did you resample the stacked image? If so then I suggest you resample each sub separately then stack using star alignment (not unaligned even they may be no drift).
The result looks very good by the way ...
Robert
I think that is looking quite detailed John
Hi Robert - yes I did a 200% upsample on stacked image in PS. Never thought of resampling individual subs before stacking.. I will give this a try - Cheers & thks Fay, John