Sunset, Tahiti.




Recently I have become involved in astronomy and imaging the night skies. Given we have many clear and acceptably dark skies North of Tucson, I am surprised I hadn't picked up a serious telescope earlier. Combining interpretation, astronomy, photography, and image processing skills to develop pictures of our night skies is enjoyable and challenging. It amazes me that I can attach a digital camera to a telescope and photograph a galaxy that is barely visible to my eye in the night sky. So far I have learned that capturing acceptable images of deep space objects is not easy, and that you can endlessly come up with missing techniques, equipment, and location limitations that prevent an improved image.

In summary though, a few things I have learned so far on astro imaging:

1. It's more challenging then I expected.

2. The lower the f stop, the better for beginner astro-imaging efforts. Lower f stop means larger aperture, and that means more light reaches the camera each second the shutter remains open. f2.0 allows almost 30 times the light that f10 does. So in a 30 second exposure at f2, I gather as much light as a 15 minute exposure at f10. And shorter exposures are much easier to achieve then longer exposures (covered below).

3. Stacking images results in a better picture then any single image. CCD sensors pick up noise that comes across as a grainy appearance, especially in long exposures. One method to conrol noise is to take several pictures, register them perfectly then digitally 'average' the set. Real image detail builds at a faster rate then noise, which fluctuates from picture to picture, thus increasing signal to noise ratio.

4. More exposure time = More detail. For Orion's Nebula, I took 8 images at about 30 seconds each, combined them, and was initially pleased with the results. Following suggestion, I next stacked 16 pictures, and found additional nebula detail emerge.

5. Longer exposures require more careful and involved telescope tracking. My current telescope is level on a tripod, otherwise known as an Alt-AZ set up. Because of the Earth's rotation, in an Alt-AZ configuration, I can usually get away with 30 second exposures before stars start trailing. For longer exposures, the base of the telescope needs to be angled towards the North Star, or in other words the axis of Earth's rotation. Doing so allows longer exposures while tracking stars correctly, and the ability to image fainter objects. Very long exposures (e.g. hours) require critically careful set up, taking into account items like balancing the telescope's center of gravity and insuring simple things like loose cables don't jerk movement as the telescope tracks a particular object. For now, I am in the 30 second exposure camp.

Any comments are always welcome, feel free to e-mail me at: