The Whale & The Hockey Stick
Description: NGC4631 & NGC466, the Whale & the Hockey Stick galaxies respectively, are located in the constellation of Canes Venatici. This image was taken on February 19, 2009 from my home in Snohomish, Washington.
This is a second light test of my new Hyperstar lens on my C14. This lens from Starizona allows me to image with my 14" SCT at F/1.95. This gives me focal length of 682mm (measures by astrometry.) The system is fast enough that typical subexposures can be 30 seconds or less. This particular field is in an area with relatively dim stars, so I was able to go 180 seconds deep.
This image has a couple of problems that I need to work on.
The most obvious is that the color is shifted towards the magenta. This is the result of my twiddling with curves on the color channel. As imaged, the galaxies were too yellow. I attempted to fix this by boosting the blue channel in the ranges visible in the galaxies using curves. I'm not happy with the result and will do some more studying on how to deal with this kind of issue.
The second issue is that there is a faintly visible dark ring around the center of the frame. The optical system that I am using results in fairly prominent vignetting. This has not been a problem with the first couple of images and flat frames corrected it. In this case, the center of the vignetting moved visibly from subexposure to subexposure, so application of flats resulted in incorrect calibration. I used GradientXTerminator to deal with the problem the best I could, but I was not able to eliminate it without severely clipping the background.
I don't know what caused the problem from frame to frame, but I suspect that there was light reflecting off the dew shield that changed over the course of the exposures. Maybe.
Equipment: The image was taken with a 14" Celestron C14 telescope on a Celestron CGE mount. The camera was an SBIG ST10XME with Astrodon filters. The exposures were guided with the ST-10's internal guide chip. Focus was done manually through the stock C14 focuser using CCDInspector's FWHM Monitor to aid in evaluating critical focus.
Exposures: 20x120 seconds each luminance, red, green and blue exposures binned 1x1.
Processing: Image capture was done with Maxim/DL 5. Calibration, registration, noise reduction and stacking were done in CCDStack. Curves, levels and zone processing were done in Photoshop CS2. Gradient processing was done with GradientXTerminator.
Click on image for full resolution.