“How to Capture a Comet”
by John Chumack
You can capture comets with either a film single-lens reflex (SLR) camera or a digital SLR camera and camera lens, too, but if you just want to see the comet visually, skip to the link below. For a recent image, I used a Canon Rebel XSi digital SLR with a Canon 75–300mm lens set to 280mm. I set the focal length at f/5.6 and the ISO at 400. I took four 4-minute exposures and combined (stacked) them to make, essentially, a 16-minute image.
If you don’t have a 280mm lens, don’t worry. I captured Comets a 28mm and 70mm lenses as well. Many comets are large, so it can look good through a “normal” lens.
For my images, I use a tracking (motor-driven) telescope mount. Again, if you don’t have a tracking mount, use the basic “camera on a tripod” method. Shoot the comet from a dark site away from city lights for best results. Make sure your camera is mounted solidly on the tripod.
Set your camera to “bulb” or “manual,” and set the film or DSLR speed to ISO 800 or ISO 1600. Set the lens’ f-stop to f/4 or lower. Focus the lens to infinity, or simply focus on a bright star. If you are using an autofocus lens, turn the “Auto Focus” setting off. Auto focus will not work properly with night sky shots anyway. That’s why it’s best to focus manually on a bright star. Once you have focused, don’t touch the lens. Carefully point the camera toward the comet.
Don’t know where the comet is? You’ll find an interactive chart at Astronomy.com’s StarDome.
Use a cable release or a self-timer to start the exposure. Avoid touching the camera. Vibrations will blur the image. Now take ten 30-second exposures of the comet. If you get star trails (stars that look like lines), lower each exposure time to 20 seconds and take 15 shots instead.
Film users develop and scan your negatives. DSLR users can just transfer the images to your computer. Next, find and use free image-stacking software like Deep Sky Stacker, Nebulosity, or Registax (Google them) to create your own 5-minute exposure.
Stack all of the images using the stars as your reference point. If the stars appear too faint, use the comet’s nucleus instead. Once you combine the exposures into one image, you can do the final level and color adjustments in your favorite image-processing program.
Congratulations! You have just captured a piece of astronomical history — a once-in-a-lifetime view of a Comet that you can share with friends and family members.
Here is the link to the tutorial I wrote for Astronomy Magazine for capturing Comet Lulin back in Feb. 2009
http://cs.astronomy.com/asycs/blogs/astronomy/2009/02/27/you-too-can-photograph-comet-lulin.aspx
Below is my shot of Comet Lulin captured with a Canon Rebel Xsi & 280 mm lens.
Comet Lulin captured with 280mm lens
This is a 40 minute exposure (ISO 400)with a Canon Rebel Xsi & 5 Inch diameter Telescope.
