Wednesday, May 16, 2012

The (Leo) Luminance Triplet

For such a dry winter, California didn't have a lot of imaging-quality skies in early 2012. We had some late-season rain and mountain snow, which was good for our hydro balance, but not so good for the spring galaxy season. I finally got out in mid-May, and spent a couple of nights shooting M65, M66, and NGC 3628, otherwise known as the Leo Triplet. Here's the result, sized for a 15" MacBook Pro screen:

This is what's known as a `luminance' image, which means it was shot with a black-and-white (or `monochrome') CCD camera, through a clear (or `luminance') filter. In order to make a color image, I'll need to shoot it through 2 or 3 color filters. If all goes well, I hope to shoot it through Red, Green, and Blue filters before the spring season slips away. The subexposures for this image were each 5 minutes long, and I shot about 50 of them over two nights, for a total exposure time of about 4 hours. As always, the imaging scope was an Orion ED80 f/7.5 semi-apo refractor.

This was also the inaugural imaging run for my new (to me) Losmandy G-11 mount. I got a great deal on it from a fellow Bay Area imager, and I spent the April dark-moon period learning some of the ins and outs. I feel like I can polar align, acquire targets with the Gemini 1 (Level 4) goto system, and I can get pretty good autoguiding. During the nights when I shot these luminance frames, the RMS error on my guider corrections was running about 1/2 pixel in both RA and Dec.

I processed this image in Pixinsight, making use of the new Batch Preprocessing script. Very handy! Many thanks to the folks who wrote that script. Also many thanks to Mike Schuster for writing the PSF Estimation script, which auto-picked hundreds of stars and gave me the parameters of the point-spread function, which I used for Richardson-Lucy deconvolution. (Deconvolution is a sharpening routine that I used to bring out some of the details in the galaxies.) The hardest part of the whole processing workflow was the noise reduction, which I did with Multiscale Median Transform. Once I had the noise somewhat beaten down, I could get a halfway-decent stretched image from the Histogram Transformation. I did a bit of HDR Median Transform, but not nearly as much as I might use on, say, a large bright nebula.

I hope to be able to get out and shoot some RGB color data if I'm lucky; it would be nice to add color to these galaxies!

No comments:

Post a Comment