Astro Bob blog: Try astrophotography point-and-shoot styleBreak out your trusty budget digital camera and head out under the night sky. Here are some explanations and tips on how to shoot your own astrophotos.
By: Bob King, Duluth News Tribune
Try astrophotography point-and-shoot style
Can you find Venus in this busy photo? Saturday night I was covering women's roller derby and looked out from level 3 of the parking ramp toward downtown. There above the skyline was Venus -- and it was darn easy to see around 8 o'clock. Bright enough to hold its own despite competition from the city lights.
I decided to take my own advice last night and use a point and shoot camera to photograph the constellations and the moon. I'm always exhorting the readers of this blog to do the same. Normally I use a high-end digital camera which gives me an unfair advantage. Time for a reality check. I grabbed one of our "reporter" cameras from work -- an 8 megapixel Canon PowerShot that cost about $300 -- and put it through its paces last night. Would it pass muster for astrophotography? I'm happy to say the answer is YES.
The first photos were taken through the telescope by holding the camera directly over my lowest power eyepiece focused on the crescent moon. Everything was set to auto, and while the images were sharp, they were overexposed (picture at right). Time to go to manual mode. After pushing a bunch of buttons -- I didn't have the instruction booklet with me -- I located the manual setting and soon learned how to adjust the three essentials: the ISO or light sensitivity, the f-stop or aperture opening of the camera lens and the shutter speed.
ISO refers to the sensitivity of your camera's sensor to light. The higher the number the more sensitive to light. If you punch in a high ISO number, say, 800 or 1600, you can take pictures under nighttime street lighting. Low ISOs are ideal for daytime photography. You might think that keeping it on high all the time's a good idea but you'd be wrong. The higher the ISO (sensitivity), the more graininess or noise in your images, and this gets especially ugly when you enlarge the image. The colors aren't as saturated and smooth either.
Ah, much better. Frankly I was astounded by how nice the image was and amazed that I didn't need to do any special focusing. This photo was taken at 48x by holding the camera above the telescope eyepiece. Details: ISO 100, f/8 at 1/125". Photos by Bob King
Since the moon is quite bright I set my ISO at 100 (low), f-stop to f/8 and shutter speed to 1/125". The f-stop determines how much light the lens lets through and ranges from around f/2.8 to f/16. The higher the number the tinier the lens aperture and the less light that reaches your sensor. F/2.8 uses the full aperture of your lens and lets in the maximum amount. For time exposures of the constellations at night f/2.8 is the way to go. The final variable -- shutter speed -- is fairly self-explanatory but it's important to know how long your particular camera can leave its shutter open for time exposures. My little guy goes up to 15 seconds, just long enough for constellation photography.
Closeup of the Theophilus-Cyrillus-Catherina craters from left to right across the center of the picture. Each of the three is about 60 miles in diameter. The magnification was 152x.This is another hand-held photo over the telescope.
After a few pictures at low power (48x), I plunked in a different eyepiece that gave me 152x. Since the field of view at higher magnification is narrower, it was trickier to get the camera in just the right position above the eyepiece to take in the smaller view. After a few tries though I got it and the results were very pleasing.
The moon at maximum zoom using the camera alone. The lunar seas as well as numerous craters near the moon's terminator are visible.
OK, it's great that I have a telescope but if you don't have one, how about a picture of the moon with the camera's own zoom lens? I placed the camera on a tripod, pulled the zoom lever to maximum and centered the moon on the focusing grid. Here's where I ran into trouble. The camera had a tough time keeping focus on the moon -- it zoomed back and forth seeking its target. After some trial and error, I managed to catch a few images at best focus. As you can see, it's not nearly as clear as those through the telescope but you still make out craters along the terminator. I plan to work more with zooming the next clear night because I think I can do better.
A 15-second time exposure of Orion (upper right) and Sirius (left edge) from last night. The lens was set to f/2.8 (widest) and my ISO was 800 with the camera on a tripod.
Finally it was time for a couple constellation photos. Because the stars are much fainter than the moon, I changed the ISO to 800 for high sensitivity to light -- but not too high to make the images look overly gritty -- and set the shutter to its maximum exposure time of 15 seconds. With camera on tripod I exposed Orion and then the Big Dipper. Again, another pleasant surprise. I actually got images. To be sure, they're grainier than than those in my high-end camera and I don't have the ability to go beyond 15 seconds but I'm not complaining.
The Big Dipper with the same setup as above. It's pretty grainy and there are tiny digital artifacts on the stars. As the sky gets brighter with the waxing moon, the photo possibilities will improve.
It helped to have the moon in the sky at the time because it provided enough illumination to outline trees and buildings. As the moon waxes toward full phase, the sky and landscape will become even brighter making for better constellation photography for basic digital cameras. The key is to first set your camera in manual mode and then adjust the f-stop and shutter speed as needed. Since you get instant feedback by looking at the view screen on the camera back, you can adjust your exposures through trial and error to get the best images possible of your subject.
Feel like trying a little astrophotography yourself? The next week under a brightening moon is a perfect time to do it. If you get one you like, please send it to me at email@example.com and I'll share it with our readers.