M101

[NoelC]

Finally
After sorting out the flats (camera was loose giving rise to offset on flats) and having read the manual on ASTAP I managed to produce an image (of sorts):-

M101 May 20th 2020.   
Taken on an Altair RC at f8 using Atik One 6.0; 20 100S bin 2x2 subs L, 10 each RGB bin 3x3 at 100S.
After watching the youtube session on sub length and background noise I radically reduced my sub length and CCD cooling (to 0°C).  Colouring is notional rather than literal (nudged the sliders around until it looked more reasonable).
The really good discovery was that ASTAP would stack the lot in one hit and register the different sized subs into an LRGB composite result. In stacking you can tell it to classify by image filter, flat filter and exposure time (I added one second to the L_L and D_L files EXPTIME using the FITS Variable adjustment in ASTAP so that it picked up the correct dark file).

[The Thing]

Nice pic Noel.

I like ASTAP it stacks subs others despair at, and produces great results.

[MarkS]

It's actually come out quite well.  The core looks really good.

The outer arms of M101 are always difficult because they are surprisingly faint.  M101 is a tough cookie.

Mark

[Carole]

Excellent Noel, it's come out really well.  As Mark says it's a tough one, and one I struggle with.
Even more surprising given the relatively short length of your exposures and using a CCD camera. 

I'd say this was your best image yet.

Carole

[NoelC]

Thanks Duncan, Mark & Carole.
All we need now is a break in the clouds!

Carole; the data was very low down; I think all my subs have very low signal. By the time I had stretched it the outer arms were within 3 adu of the background and un-stretched the sub was completely black.  Is it to do with the way I stack it?  I just put it on sigma clip/ star align and let it do it's thing.  Can extend the exposure time, but the stats say S/N won't improve and frame mortality due to tracking, seeing and satallites(!) increases, so am inclined to stay short.

Struggling a bit with my clapped out old version of Photoshop (and I refuse to pay £20/month or whatever the current version costs), did a youtube tutorial on using GIMP which was very useful:-
https://www.youtube.com/watch?v=fSxdHrO0zfU
27 mins, good intro to the package and use of levels, curves, layers, star masks and selective contrast.

Noel

[Carole]

That looks a good tutorial on Gimp, I only tried to use it once when I was in Spain and hadn't put Photoshop on my mini laptop.  Couldn't get much sense out of it at the time but this tutorial is good.

What version of Photoshop do you have Noel, I am using CS3 and there is only one thing I have found on a new tutorial that I can't do with it.  I bought mine years ago on Ebay as used old version. 

Carole

[NoelC]

Carole
I have CS2.  I bought CS3 second hand (CD, box and manual £30 - if anyone's interested) but the software wouldn't fire up (complained it needed updating) after many hours of hunting on Adobe archive websites it sent me to the old CS2 version.  I also have PSE5 (circa 2005) which is more use than CS2 - but doesn't support curves.  I think I'm a GIMP convert now.  It opens a lot more raw files, although when opening 32 bit FITS files it imported them as greyscale.
Just remember the Levels and curves are under the 'Color' menu.
GIMP tip of the day: to Deselect CTRL+SHIFT+A.
The History pane is in the multi-use pane on the left (Device Status/History/Images pane), but you can step back with CTRL+Z forever.
Noel

[RobertM]

That looks really good Noel, much better than my first effort !  Plenty of detail towards the core and the outer arms are starting to show.

Robert

[Roberto]

Great result Noel. Plenty of detail all the way to the core.

Roberto