Cassiopeia Observatory

D7000 DSLR Imaging: NGC7479 Spiral Galaxy

Posted: 14 October 2012

The observatory was opened Saturday, 13 October 2012, at 1749 MST, 79°F. The sky was clear. At 1756 MST, 4 minutes after sunset, viewed Mercury, low in the west, at 77X and 206X. The disk was visible but seeing was not good due to the planet's low altitude above the horizon. At 1810 MST, Mercury became visible to the naked eye, if you knew where to look. I lined up two finderscope mount screws to point the way towards Mercury.

I then began preparing the D7000 DSLR for the night's planned astrophotography. Once that was done, viewed Mars at 1820 MST, 77X; no details visible. At 1839 MST, slewed to the night's imaging target: NGC7479 (spiral galaxy). My plan was to take multiple 2 minute, ISO 6400, exposures for stacking using Lynkeos. At 1850 MST, the galaxy became faintly visible at 77X. By 1906 MST, the sky was dark enough to show the galaxy nicely at 77X. I mounted the DSLR at prime focus of the 8" LX200-ACF using the Off-Axis Guider (although I did not plan to manually guide during the exposures). Did a focus test on the star Alpha Pegasus using the Bahtinov Mask. At 1917 MST, did a 1 minute, ISO 6400, framing test exposure of NC7479. Next, I did a 2 minute test exposure to check how accurately the LX200 was tracking. I could detect no trailing in the image so decided to take the multiple exposures at 2 minutes, ISO 6400. I then did 20 2 minute exposures using the Vello Wireless ShutterBoss Timer Remote for camera shutter control. After the first 10 exposures were completed, I powered off the camera for 10 minutes to provide a sensor cool down period. I then captured the next 10 exposures. I completed imaging at 2026 MST.

During post-processing of the 21 2-minute exposures, I discovered that many of the images had slightly trailed during the exposures. After tossing out the trailed images, I ended up with 7 good images for stacking. This first image (cropped) is one of the 2 minute, ISO 6400, exposures that were used for stacking:

This next image of NGC7479 is a stack of 7 2-minute exposures, yielding an effective exposure of 14 minutes:

More of the galaxy is visible in the stacked 14 minute image than what was captured in the single 5 minute, ISO 6400, image shown on my previous report.

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