D7000 Imaging: Crescent Moon, Star Spectrum Tests
Posted: 22 June 2012
Wednesday, 20 April 2012, the sky was covered by thin high blue-white smoke, apparently from a fire in eastern Arizona. No observing. Thursday, 21 April, started out clear but clouds, haze, and some smoke appeared mid-afternoon. By sunset, things looked better. Opened the observatory at 1910 MST, 102°F. The sky was mostly clear, with some clouds low in the west, but still somewhat hazy. At 1918 MST, viewed Mercury, low in the western sky, 77X and 206X. Had a good view of the about 50% illuminated phase. Even 364X showed a nice view at times.
At 1922 MST, slewed to the thin crescent moon and briefly vieweed it at 77X. Features were clearly visible against a bright sky, still 12 minutes before sunset. As I was making some notes, I briefly saw a very large quail family walk by the observatory. There were at least 12 chicks in addition to mom and pop quail. I then set up to image the moon. I removed the star diagonal and switched to the visual back for 8" LX200-ACF prime focus imaging with the D7000 DSLR. At 1941 MST, I took a series of images against a still bright sky. I took another series beginning at 2000 MST against a somewhat darker sky. This is a 1/250sec, ISO 1000, exposure from the later series:
I removed the camera and switched back to the star diagonal for some lunar observing. Used 77X, 133X, and 206X. While I was making some notes about the lunar observations, a Kissing Bug landed on my shirt sleeve! That was the first time in 3 years of seeing them here that one has actually landed on me (that I know of). I knocked him off and never saw him, or any others, again.
At 2018 MST, viewed Saturn, 77X and 133X. Seeing was not very good. Three moons were visible: Titan, Dione, and Rhea.
At 2027 MST, slewed to the star Spica and began setting up for some spectrum imaging tests with the "Star Analyzer". I have been concerned that many of the spectral lines that I have captured in the past were not actually lines, but artifacts from digital noise in the images due to the high ISO and short exposures necessary. This night I would take some high ISO images for comparison to my earlier images. I used ISO 1000 this night. I also decided to ensure precise focus by doing a test exposure using the Bahtinov Mask. This is the interesting image with the mask:
I then did a series of exposures (without the mask) of the star Spica (Spectral Type B1), from 1 second down to 1/40sec. The best was one at 1/20sec, ISO 1000. This is the processed image, showing some "lines":
Compare the above image to one I did in April 2012 at 1/10sec, ISO 2000:
There are obvious differences.
I slewed to Vega (Spectral Type A0) and repeated the tests. This is a 1/30sec, ISO 1000, exposure:
Compare that image to one from October 2011, 1/30sec, ISO 1600:
Again, there are differences.
I plan to do more tests using a much lower ISO but longer exposures on my next session. I'll see if the results improve.
Closed the observatory at 2056 MST, 84°F.
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