Thursday, 24 September 2020

Lockdown Astrocamp 2 - Another One Gets Away

 Lockdown Astrocamp 2 - Another One Gets Away

Earlier this year, I wrote about missing out on one of my highlights of the year, the Astrocamp star party.  Though gutting, cancelling it was the sensible, and only real choice.  Possibly through rose-tinted glasses, everyone looked forward to and hoped that the second scheduled event in September would go ahead.  Alas, continued developments have conspired against the organisers and us, to leave little option but to pull the plug on the Autumn event too.  But it takes much more than a microscopic organism to stop us from doing any astronomy! 
Readers of my past posts will know that we often do battle with the weather at Astrocamp.  More often than not, not much astronomy gets done but everyone still had tons of fun.  This time, should we have all been gathered at Astrocamp HQ, we would of had a straight run of clear nights for the whole camp.  Typical!  So, what do you do with a few days of work, a run of clear nights and a plenty of time?  Get out there and make the most of it of course!

What was it I did before?????

After a comparatively short amount of time out of the observatory (about 2 or 3 months in total) because of weather and generally Summer getting in the way, it's been awesome to get back in there again.  The first clear night was always going to be a bit of a struggle.  Trying to remember how things worked, what settings I used where. and how it all comes together was always going to tax the brain a bit.  That coupled with high cloud whipping across the sky occasionally meant that any thought of getting hours of data on a target was going to be tricky.  Best start basic and build back up I thought.  Gradually, it all come back, and I was able to get polar alignment tidied up, updates installed, get guiding going and eventually grab a few frames of a target.  That'll do for one night.

17th September and NGC 6992

Cygnus is high in the sky at this time of year, and has some truly awe inspiring targets to chose from.  Perhaps the most photographed is the Veil Nebula.  The nebula itself is a huge target, impossible to fit into a single frame of my camera and telescope.  It's obvious why people hone their mosaic skills in this area of the sky, taking sets of data from all different regions of the nebula before stitching them all together in post processing to give one image of the whole area.  I'm not at that stage yet. I wouldn't know where to start, but I did get around 3 hours of data on the Eastern Veil.  That would be good enough for me as a first serious swing at getting an image after the Summer break.

The Eastern Veil Nebula - Cygnus
Altair Astro 80 ED-R, Hypercam 183c and Altair Quadband filter.

20th September and NGC 281

After a few days of playing around with that data, and producing the image, I started to remember how far my imaging had come over the last winter.  There were two key things which I had in my mind to tackle next.  One of those was dithering.  For a quick explanation...
When a camera is taking long exposures, some cameras can produce a lot of 'noise' in the image.  It's particularly noticeable in the darker background where the image looks very grainy.  That in itself isn't too bad as you can remove it to a degree in post processing.  But, noise often appears in straight or diagonal lines across the image and I've seen it referred to in forums as 'walking noise'.  Due to it's regular direction, and frequency, it can be harder to eliminate during processing.  This is where the lovely term 'dithering' comes it.  Usually, the telescope and mount will track a target through the sky, and aided by guiding software like PHD2, the target is kept exactly in the same place in the frame for the whole time.  This I believe causes noise to appear in the same pattern for every frame being taken and when all these frames are stacked on top of each other, the walking noise pattern is formed.  Dithering combats this, so it was time for me to learn how to dither effectively.  By luck, it's extremely simple to set up within SharpCap.  A couple of ticked boxes, and a slight amendment to the way I set up my imaging runs, and I had it working.  Dithering now moves the camera on the mount a tiny amount, even just a few pixels, in a random direction in between every few frames.  It means that because the target, and therefor the background has moved slightly in relation to the rest of the frame, that the camera sensor isn't putting all the noise in the same place.  During stacking, PixInsight takes the stars in the image as fixed points, and overlays the images using those stars as reference points.  Any noise produced is therefor not concentrated in the same place every time, and therefor isn't so apparent in the final frame.  Perhaps one day I will do a more illustrative post on that, but it is a pretty basic tactic used in imaging which I should of learnt how to do and adopted from the start.
Nevertheless, dithering sussed and slightly less noisy data to process, I pointed the camera to NGC 281, the Pacman Nebula.  This is a target which I have imaged last around 2 years ago.  This was the result then:
Since then, I have invested in a new filter which isolates emissions of different light wavelengths very effectively.  It brings a whole new appearance to the final image.

Pacman Nebula - Cassiopeia
Altair Astro 80 ED-R, Hypercam 183c and Altair Quadband filter.

21st September and NGC 7635

The last night in a run of good nights for observing and imaging.  The great thing with having an observatory is that it gives me time to get everything on and imaging within around 10 minutes of opening the door.  After that, I'm free to get out the SBT (12" dob) and return to good old fashioned visual astronomy.  This time of year is awesome, especially at the moment where we have Jupiter, Saturn and Mars easily visible, with a couple of other planets visible if you know where to look.  With the Summer constellations visible for a few hours at the start of the evening, it's awesome to be able to see the Witches Broom nebula, the Ring Nebula and loads of the classic clusters.  If you hang around until the small hours, you then start to see the arrival of the more traditional Winter constellations like Orion.  I've also been lucky enough to provide some neighbours with a very quick whistle stop tour of the sky and it's been absolutely brilliant to hear their reactions the first time the clapped eyes on Jupiter and Saturn.  Hopefully something that will stick with them all for a long time.
Back to the imaging.  This quadband filter is making a big difference to my final images and I wanted another opportunity to compare a target imaged with just a light pollution filter (which filters out predominantly sodium, leaving many other wavelengths of light through) to one taken with the quadband.  So, I  looked back through my blog, and picked up NGC 7635 also know as the Bubble Nebula which I first images around 2 years ago.  I collected a very similar amount of data (around 3 hours ish) with the same camera.  This time though, the target seems to "pop" out much better.  It's a small target in the frame, and with hindsight, perhaps I should crop the high resolution image and enlarge it a little to help bring out more of the detail.  The new filter does seem to being out much more red, and fainter nebulosity is definitely more visible surrounding the bubble itself.

Bubble Nebula - Cassiopeia
Altair Astro 80 ED-R, Hypercam 183c and Altair Quadband filter.

Wrapping it up.

Earlier I mentioned that there were two things at the end of Spring into Summer, that I wanted to get to grips with.  On of those was dithering.  Tick.  The other is processing data captured with the quadband filter.  I use PixInsight as my primary software for stacking and processing, but it is quite complex.  I've heard and read of many people splitting their image up and doing some whizz bang processing on the different channels before combining it all back together again to give amazing results.  The bit that I can't find is a step by step guide for that part of the process using a OSC and quadband filter.  I've got a vague idea, but nothing solid which produces the results I expect.  That's my next objective, and one that I hope to have sussed in the coming weeks.  We shall see!
Until the next time, thanks for reading, and clear skies.

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