Friday, April 8, 2011

2011 Astro Season starts...finally!

Finally some clear, decent skies!!

That was a good opportunity to check the equipment: you never know what kind of gremlins might be waiting for you when you plug in the power. The first challenge I had to overcome was an unusual one. I looked everywhere and my counterweights were nowhere to be found. Then a suspicion...I must have left them on the ground of my backyard before the big snow came and now they were buried under 3 feet! I dug around the places where I usually setup and eventually the shovel hit treasure: found them! 

The second challenge was testing a Celestron NexGuide autoguider. I am trying to sever the dependency of my astroimaging from my laptop. My current autoguider (an Orion Starshooter) requires a USB connection and guiding software to run. I was quite intrigued by the possibility of having a standalone autoguider so I took the plunge. So far I can't say I am's a nifty unit, but I can't get round star...yet (I hope). Instructions say that it works well with guidescopes of 80mm aperture or larger and focal length between 400mm and 1200mm. My Orion ShortTube is 80mm/f/5 so 400mm in focal length. Perhaps guiding is not great because I am at the very limit of the range. Next time I will plug in a 2X Barlow and see what happens. I am concerned however that slowing down the guidescope to an f/10 I might not be able to find a decent star in the smaller field of view. We'll see.

The third challenge was to get my old autoguider to work. For some reason I could not get it to work properly. Eventually after some vigorous clicking and cursing it started working again. It probably needed some encouragement...

Being the optimist I am I wanted to give a try to the Leo I Dwarf galaxy, very easy to find as it is only few arcminutes away from Regulus. Leo however was getting too close to my neighbour's sequoia-like trees so I settle for something more comfortable still firmly planted in the Easter part of the sky: the globular cluster Messier 3.

I took the opportunity to make a change to the way I take images under a light polluted sky: instead of going for a bunch of 30sec subframes at ISO1600, I settled for 3min subframes at ISO200. I recently read a post on the Canon_DSLR_Digital_Astro by Blair McDonald who tried this and got pretty good results. What is the advantage of taking longer, less subframes keeping the total exposure the same? The idea is that a longer subframes collects more photons, that is signal. More signal is good as it improves the Signal-To-Noise (S/N) ratio (noise grows, too on a longer exposure, but not as fast as signal so longer individual exposures have higher S/N). The theory is that the final stacked image should be better. 

Here's the final image.

This is a 3min x 60 exposure (3hrs) using an unmodified Canon 450D at ISO200 at prime focus of a 8in f/4.9 (FL=1000mm) Newtonian telescope on a Losmandy G-11 mount. The exposure was autoguided using an Orion Starshoot autoguider and PHd Guiding. Stacking was done in DeepSkyStacker and processing in Photoshop CS2.  

The image is a 28.9' x 19.4' crop  (equivalent to shooting at 2600mm focal length) of the original image which spans a field of view of 76.2' x 51'. By the way: the "noise" you see around the central part of the cluster is not noise, but faint stars. The brighter, yellow/orange stars are old, evolved Red Giants and are part of the cluster located at about 33,000 light years from the Sun.


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