Sunday, 4 November 2018

2 Clear Nights - Part 1

Andromeda - M32

The end of British Summer Time is really when Astro activities begin to ramp up for the winter.  The opportunity to be observing or imaging within an hour or so of getting home after work makes the whole thing much more accessible.  It's now possible to get a good 4 or 5 hours of time at the scope and still get to bed at a realistic time on a school night.  But still, the opportunities need to be embraced when they present themselves.
So, this passed week produced 2 clear nights with steady a steady sky, and the moon not putting in an appearance until the early hours.  As I gain more experience at this imaging game, I'm learning to push my equipment further than I have before.  Every session present a new lesson, and the first session of the week was no different.

Andromeda - The Accidental Core

M32, the Andromeda Galaxy, is well positioned in the Autumn sky, high up above the surrounding rooftops.  A very popular target, because it's big, and bright.  Sometimes it's brightness can present it's own issues which I shall come to soon.  I've imaged the galaxy several times over the last few years, but as my knowledge of processing in PixInsight and use of Sharpcap 3.2 increases, it's always a good target to revisit.  I can compare my images to previous ones and it helps remind me about how my imaging is improving.
With the usual setup and alignment tasks carried out, I slewed the scope around to Andromeda and started the process of compiling the imaging run.  All my imaging at the moment is carried out using Sharpcap 3.2.  It's got lots of great features, but you don't have to know about all of them to get imaging.  I've started with the basics of camera control (exposure length and gain), but make a point of learning a little bit more about it each time.
Framing of your target is really important.  Just as important as focus.  In my passed images from a few years ago, framing was always a bit hit and miss.  This time, I used Sharpcap to help get the core of the galaxy in the centre of the frame.  To do this, I used the auto stretch function on the display image.  It takes a single frame, stretches it to bring out the brighter parts of the target and allows you to then used the mount controls to gently nudge the centre of the target into frame.  Used in conjunction with the crosshair reticule on the image screen, framing a target image becomes really easy.  Quite simply, I can't believe that I hadn't come across this before!
So, everything framed, focussed and gain and exposure settings set up, guiding enabled and running, I started the image run.  I was aiming for 40 x 2 minutes exposures for the evening.  That left me with plenty of time to run off some dark calibration frames before packing it all in.
Around half way through the run, I noticed something on the Sharpcap software that I had not noticed before.  I didn't want to stop the run and potentially waste the data I had collected so far, so I let the run complete.
The previous session in which I imaged the Witches Broom Nebula, I started playing with binning.  I run that session binning the data 2x2.  It was successfully, and produced a pleasing image.  However, what I didn't realise, was that when those image run settings were saved, removing the binning settings later returned to the normal 1x1 binning settings, but it also produced a smaller ROI scale, or, Region Of Interest.  In effect, it allows you to use a smaller proportion of the cameras chip resulting in a smaller sized image for processing later.  It's also very useful for imaging smaller targets like planets or small nebula.
After the image run on Andromeda was completed, I stretched one of the sub frames and immediately saw what had happened.  Andromeda is a huge target.  It fills the full frame, and a bit more of the Hypercam when used with the 80 ED-R.  So, the effect of having a smaller ROI set up in Sharpcap meant that instead of capturing the true expanse of the galaxy, I actually collected a load of data, more on less just of the core of the galaxy.  Now, as I mentioned earlier, the galaxy is really bright.  More often than not, the core is so bright that it appears blown out in all but the best of processed of images.  Initially, I was disappointed.  My final unprocessed, but stacked image just showed a large yellow-white blob taking up the majority of the frame.  Not wanting to waste the data totally, I went ahead with the processing anyway.  And this was the surprising result...

M32 - The Andromeda Galaxy (core).
It was a big, but pleasant surprise when I managed to reveal this much detail in the core of the galaxy.  To give a comparison, this is what the stacked, but unprocessed image looks like.  Remember that this is what I get as a result of stacking all my light frames and then performing an initial stretch of the data.  It also gives a good idea of what further processing steps achieve.

M32 - Stacked and Unprocessed.
In particular, the core is no longer a white blob, and individual stars and dust lanes can be resolved.  The next time I image Andromeda, I'll be using the same settings, but ensure I'm shooting full frame images.  I'll be chuffed to bits if I get this level of detail across the whole image.  Definitely one for the to do list!
That's Part 1 of this post done.  In the next part, I'll be looking at the results of the second clear night from last week.  Until then, cheers!

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