April 13, 2013 Leave a comment
The constellation of Orion is always an interesting region to photograph for amateur astronomers. A large collection of dust bands and nebulas scatters around the Orion’s Belt, the triple star in a slanted row cross the middle of the constellation. The most visible ones here are Orion’s Nebula M42. Beside it sits the running man nebula NGC 1977, resembling a man running into dust cloud. In the lower left of the image are the Flame Nebula and the Horsehead nebula in red.
This image was taken back in December 2011 when I got my brand new D7000. A total 64 minutes exposure was obtained by stacking 360 seconds individual light frames. A set of flat frames to correct vignetting and dark frames are also used in calibration. I was immediately surprised by the noiselessness and high sensitivity of D7000 compared to my old D200, which is severely hampered by amplifier glow from all corners and high shot noise because of low QE.
In 2012, I had converted my D7000 into an astrophotography capable camera by replacing the color correction filter with a clear optical glass. The result is nothing but spectacular. In the following shot with the same aperture and ISO setting, a mere 18 minutes total exposure could achieve a similar signal-to-noise ratio in the H-alpha region. This only accounts for 30% exposure time comparing to the first one. And I also need to mention that the sky background is higher in the image below, which will contribute significantly to the noise in dark regions. If a comparable exposure is done with light pollution rejection filter, you could expect much better result for the image.
One caveat is that more noticeable glare and halos from bright stars, which is result of internal reflection of uncoated clear glass used in conversion. If you could obtain a 1.1mm thick glass with broadband coating, this effect will be greatly suppressed. Also you need to retain the dust filter with its IR reflecting coating. This will help you reduce the infrared spectrum from light pollution.