Posted in Astrophoto Log on September 28th, 2008 by Northwest Astro
Last night, the clouds broke and let me back under the stars in this light polluted suburb. I’ve been itching to use the small refractor on the Double Cluster for a couple weeks now, after I first attempted to get an image using the larger 10″ scope, and realized the two clusters together just don’t fit. Focal reducers help, but you are literally filling up the whole frame, which gives you no wiggle room when it comes to light falloff on the edge, or cropping away artifacts from stacking images together.
Draft
Processed
I managed to get roughly an hour worth of exposures with nearly perfect tracking, despite a rough alignment, and still tracking in Alt/Az. Unfortunately, I forgot to bring out the dew shield for the 10″, so after the images were taken, there wasn’t much hope for doing any visual observing with the big scope. I took my dark and bias exposures before heading in for the night.
This morning, I’ve been cobbling together the work from last night, running the data through pre-processing, and using the Drizzle stacking method for the first time in Nebulosity. I’d say the results turned out rather well after letting it grind on 85 images 12 Megapixels in size. With a DSLR, I find that you really don’t want to let Nebulosity scale your image up too much, as you already have an awful lot of pixels available.
I’ve posted two results. The first is my draft image of the Double Cluster, where most of the work after the stack was done by manually setting white balance and adjusting levels. The second is the more heavily processed version where I let Nebulosity try to filter out the skyglow for me before adjusting the levels, and I more aggressively cropped the clusters. You can more easily see fainter stars in the second, more processed image. Unlike most, I don’t like blowing out my stars to make the faint stars brighter and instead go for a more ‘faithful’ approach, and unfortunately that does have the effect of keeping the faint stars darker. Because the shot was taken at ISO 1600, it does still have a fair bit of grain in the image even after processing with a fairly sizable stack of darks. I am still learning a bit, and may revisit these particular images in the future when my post-processing skills get a bit better.
