Tuesday, September 30, 2008

Return To The Moon

It's been a while since I last pointed my trusty ToUCam Pro webcam at the Moons surface - too long to be honest! I find there's something very satisfying in this day and age of expensive equipment of putting a humble webcam at the prime focus of my telescope. The instant gratification of seeing a small section of the Moon surface shimmering away on your laptop screen cannot be underestimated in my book!

I was having a torrid time with my 20D's first outing - I always forget something, and this time it was the USB cable to connect it to my laptop for long exposures. The night was superb, and once the Moon had risen over the observatory dome I couldn't help but have a go at imaging it "for old times sake", plus I know that at least I could take home something good from the night!

Times have changed since I first started webcaming - we can now update the firmware on the ToUCam to remove the automatic sharpening, and even remove the automatic debayering algorithm as well. The result? Much smoother, sharper images that give fantastic results. Unfortunately I did not pay enough attention to getting the correct exposure :( It's all too easy with the Moon to get this wrong due to its huge dynamic range - ideally you should take a number of exposures and blend them together to get best results, but on this night I as just wanting to grab a quick image. I really should learn that this is not a good idea! Anyway, here's the resulting image:


Still, I'm impressed with the result. Another great thing about webcams is that a mosaic stacks up the mega-pixels pretty darn fast! Back in 2002 I spent an evening with my 8" Meade Starfinder and 2x Barlow lens capturing over 60 sets of avi files to produce a massive image that I had printed out and now proudly hangs on my wall at an impressive 2 foot square. I think it took me well over a week to process that bad boy! It's like having my own personal Lunar Atlas on the wall, and I love it :)

Anyway, back to this image! Now, I don't know why, but Registax really, really, winds me up! It just never quite works the way I want it to. For this image I simply wanted to multi-point stack all 8 frames using sigma clipping. I gave up on the multi-point aspect as it just did not work :( I'm not sure I really needed it anyway for this project. The stacked images were then dumped into Photoshop, clipped to a clean edge, feathered out, and mosaiced together. I used the exposure image adjuster to level out the variable transparency that occurred during the capturing process, and a liberal use of the eraser tool removed a few alignment oddities. With a clean base image, I ran the smart sharpen filter to bring out a bit of the detail (I'd love to use a deconvolution filter in Photoshop, but I don't have one) and then ran three sets of high-pass filtering of reducing filter size (7.5, 3.2, 1.4) to increase the tonal range and contrast without introducing too much noise into the final image. The end result, a rather pleasing lunar mosaic and an urge to do it again - but this time properly :)

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