Shoot the Sky Without a Telescope

Shoot the sky without a telescope

These simple techniques will help you capture great pictures with just a camera on a tripod. by Michael A. Covington

The Moon rides high in the sky next to brilliant Venus while fainter Jupiter (immediately above the power pole) lurks near the horizon. The photographer took this 8-second image at f/3.2 and ISO 80. Tom Faber

possible (f/2.8 in many cases, but use f/1.8 if you have it), carefully set the focus to infinity, and expose for about 5 seconds. View the resulting image and see what you’ve got. You’ll find that if you expose longer, say for 30 seconds, you’ll get more stars, but they’ll appear as streaks because of Earth’s rotation. Yet if the exposure is too Rich star clusters, glowing gas clouds, and dark dust lanes enhance this image of the central Milky short, you’ll get only a few stars on a Way taken through an 11mm f/2.8 lens. The photographer created this photo by stacking eight pitch-black background. In the old days, 30-second exposures at ISO 800 and seven 30-second exposures at ISO 1600. Luis Evangelista A camera on a tripod stands ready to capture a colorful aurora. Martin Ratcliffe photographers had to calculate the maximum exposure time before the stars started to streak, and this time varied ne of the biggest barriers techniques to make the most of basic, by today’s standards. With a digital cam- depending on the section of sky being holding back budding inexpensive equipment. era and current software techniques such shot and on the lens’ focal length. Today, astrophotographers is the as image stacking, however, almost any- with instant results from digital cameras, belief that they need a Shooting the stars one can capture far better images than I it’s much easier to experiment. large telescope and other I got my start in fixed-tripod photogra- managed 35 years ago. expensive equipment to get decent phy of star fields in the mid-1970s. Not To get started, all you need are a cam- Kill the vibration results. Nothing could be further from by choice, mind you. This technique was era and a tripod or other sturdy support. Your tripod does not need to be rock the truth. You don’t even need a telescope my only option when I temporarily had The best choice is a digital single-lens steady (although a sturdy one certainly to photograph the stars. Nowadays, any- no telescope at my disposal. reflex (DSLR) camera with a fast wide- doesn’t hurt) because shutter vibration one can capture beautiful images with So, I attached my film camera to a tri- angle lens. Some of the better non-SLR will last only a small fraction of the expo- just a camera and a tripod. In fact, now pod, aimed it at the stars, and exposed digital cameras also will do a decent job, sure time. If vibration proves to be a that some of the best astrophotography for anywhere between 5 and 20 seconds as will a film camera with fast (ISO 800 problem, try the old “hat-trick” tech- software is free, you can use advanced at focal ratio f/1.8. I was fascinated with or higher) color film. nique: Hold a black card (or hat) in front pictures that showed more stars than I On the next clear night, take your Longtime astrophotographer Michael A. could see with my naked eyes and even equipment outside and experiment. Aim This is part two of Michael Covington’s Covington is senior research scientist and captured a few deep-sky objects, includ- your camera at the starry sky, set it to imaging series. He will look at piggy- associate director of the Institute for Artificial ing the Orion Nebula (M42). I was happy ISO 400 or 800, zoom the lens to 50mm back astrophotography in a future issue. Orion climbs above the trees along the eastern horizon in this view from November 2009. The Intelligence at the University of Georgia. with the results, even if they were crude or shorter, set the aperture as wide as imager shot this scene with a 15-second exposure at f/2.8 and ISO 400. Tom Faber

62 Astronomy© 2011 • January Kalmbach 2011 Publishing Co. This material may not be reproduced in any form www.Astronomy.com 63 without permission from the publisher. www.Astronomy.com the sky. First, you’ll need to take manual exposures, setting both the aperture and the duration yourself. If your camera doesn’t support durations long enough, set it to “bulb” (which means “expose as long as I hold the button down”) and use a cable release to trip the shutter. Autofocus doesn’t work on stars either. Some non-SLR digital cameras will let you lock the focus on infinity (often indicated by a mountain symbol). With DSLRs, don’t trust the infinity mark (∞) on the lens; especially with longer lenses, it’s likely to be imprecise. Instead, use live focusing (Canon calls it “Live View”) if your camera has it. Center the view on a bright star and use maximum magnification to get the sharpest focus. If that doesn’t work, take some 5-second test exposures to find the best focus by trial and error. You also may want to turn off image stabilization. This feature typically works by detecting the inevitable motion in hand-held shots. But with a camera on a tripod, there is no motion. In this case, image stabilization on many DSLRs actu- Comet C/2006 P1 (McNaught) hangs like a sword above Patagonia in this January 18, 2007, photo. ally introduces motion into the final The imager captured the bright comet with a 75mm lens at f/5.6 and a 2-second exposure. Martín Moliné of the camera’s lens for the first second image. Experiment to see whether this so the camera won’t record the initial feature helps or hinders your results. shaking. You may or may not need a cable release — many digital cameras Tweak your photos will time a 5- or 10-second exposure The final step is to process the image dig- automatically and start it with a delay to itally to improve brightness and contrast. Globular cluster Omega Centauri (NGC 5139) barely clears the trees in Georgia. The author shot eliminate vibration caused by touching Don’t expect what comes out of the cam- this cluster on a single 5-second exposure through a 50mm lens at f/2.8 and ISO 1600. Michael A. Covington the shutter-release button. era to be the finished product. Back in The camera lens matters. Don’t be film days, we used No. 5 enlarging paper tempted to go with a long telephoto or for high contrast. Today, you’ll want to long zoom lens. Such lenses magnify the use Adobe Photoshop, Photoshop Ele- effects of Earth’s rotation and quickly ments, GIMP, or whatever software came turn stars into short lines, severely limit- with your camera. ing the fixed-tripod exposure time. Raising the contrast really brings out Instead, to capture a rich star field, stars. The background in the finished use a lens with a reasonably short focal picture should be dark gray, dark blue, length and a fast f/ratio (faster f/ratios or brown — not black. If you’re still using have lower numbers, so f/2.8 is faster film, find a photo store with a kiosk that than f/5.6). Many DSLRs come with will scan your negatives and let you make an 18-to-55-mm zoom lens; try it at your own prints to give you more control. 18mm to 30mm. Better yet, get a 50mm Now it’s time to see what you’ve cap- f/1.8 lens, which used to be the standard tured. You can expect to record stars and lens for film cameras. You’ll find these planets down to 8th magnitude; if you relatively inexpensive lenses deliver shoot on a dark night out in the country, tack-sharp images. the limit likely will be at least a couple of magnitudes fainter. Many of the bright Manual, not automatic Messier objects will appear, as will other The North America Nebula (NGC 7000) glows red in this image, which consists of eighty-one Many people live happily taking snap- bright deep-sky objects. Closer to home, 10-second exposures and four 8-second exposures, all taken at ISO 12,800, and then stacked. The shots in full automatic mode. But you’ll bright asteroids such as Ceres and Vesta Venus hangs between the crescent Moon and a Sun-drenched pine tree the afternoon of December photographer used a DSLR with a 135mm f/1.8 lens. Bob Post have to broaden your horizons to shoot and naked-eye comets will show up nicely. 31, 2008. It took an exposure of only ⁄ second at ISO 80 and f/4.3 to capture this scene. Tom Faber

64 Astronomy • January 2011 www.Astronomy.com 65 Camera-on-tripod imaging also is the best way to capture wide-field displays of meteor showers and aurorae. If you live south of the equator, or simply visit there, have fun recording the Magellanic Clouds, the Eta Carinae Nebula (NGC 3372), and the Jewel Box Cluster (NGC 4755). One of my deep regrets is that I didn’t try fixed-tripod shots of Crux and Centaurus during my one and only trip to Australia.

Getting rid of hot pixels If you’re lucky, your camera offers “long- exposure noise reduction.” This means that after each exposure, the camera takes an identical one with the shutter closed and then subtracts it. That gets rid of A crescent Moon passes the Pleiades star leakage from “hot pixels” — pixels that cluster (M45) March 20, 2010. The photographer think they’re seeing some light when they captured this conjunction with a 1-second aren’t. Otherwise, the hot pixels show up exposure at f/4.3 and an ISO of 200. He used as tiny, brightly colored “stars” that don’t a 10x optical zoom and a 2x digital zoom to increase the image’s scale. Tom Faber exist in the real sky. If your camera lacks this feature, you’ll A Perseid meteor flashes above Joshua trees in the Mojave Desert August 12, 2010. The imager need to take your own dark frames rotate-and-stack mode. The results can caught this meteor with a 15mm lens at f/3.8 and a 24-second exposure. Tony Rowell (exposures with the camera’s sensor cov- be impressive. This is the same technique ered) and subtract them manually. You advanced astrophotographers with motor- should shoot dark frames with the cam- driven mounts use when making their era at the same temperature and ISO deep-sky images, except that their expo- Off to the Moon setting as for your star-field images and, sures typically last for 5 minutes or more Not every clear sky arrives without the preferably, on the same evening because instead of 5 seconds. The reason software Moon. Should you stay inside and waste sensors change as they get older. It’s best has to rotate the images before stacking the nice weather? Of course not — you can to take several dark frames and let your them is because Earth’s rotation continu- always shoot the Moon from a fixed tripod. software average them so you subtract ously twists the picture and shifts it. The Moon is a trickier subject than the the effect of continuing leakage rather The software sorts all this out auto- stars, however. You should plan to use a than momentary fluctuations. matically. You can also tell it to remove lens with a 300mm or longer focal length to capture detail on the lunar surface. And The best way to take dark frames is pixels that deviate radically in one expo- you need a sturdy tripod because shutter to set the camera to take raw or TIFF sure compared with the others. This is a vibration is a formidable adversary — images and do the subtraction with an good way to get rid of momentarily hot exposure times are too short for vibrations excellent piece of freeware called Deep pixels, which are often caused by a cos- to settle down. Use a cable release or Sky Stacker (http://deepskystacker.free.fr). mic ray striking the sensor, as well as infrared remote to keep from shaking the You want to avoid taking images in JPEG airplane and satellite tracks. camera, and if you have a Canon digital format because JPEG compression blurs Sadly, it also will delete meteor trails. single-lens reflex camera that allows it, The Moon is a nice target for a camera- the position of the hot pixels. In addition, So, if you happen to be shooting during take the exposure using “Live View” (live on-tripod setup, although it does pose a when the camera converts an image to a meteor shower, you’ll want to look at focusing) so the shutter already will be challenge. The author captured this waxing JPEG format, it adjusts the brightness your pictures individually. If you capture open and the exposure can begin electron- crescent through a 300mm lens with 1.4x nonlinearly so that the subtraction no a nice meteor, save that shot separately ically without further movement. teleconverter and a ½ -second exposure Focus carefully, by trial and error if at f/8 and ISO 200. Michael A. Covington longer works as simply. If you must work and only combine the other ones. needed. And don’t trust your camera’s auto with JPEG dark frames, however, your Whatever targets you decide to shoot, exposure because it won’t realize that the This will bring out lots of detail. Finally, con- safest bet is to use BlackFrame NR soft- be persistent and willing to experiment. background needs to be pitch black. A sider raising the color saturation to bring ware (www.mediachance.com/digicam/ The sky offers stunning views on any good starting exposure for the gibbous out the slight blue of Mare Tranquillitatis, blackframe.htm). clear night. You can capture many of Moon is 1/1000 second at f/11 and ISO 800. the green of the other maria, and the pink them with nothing more than a good Process the image with the “sharpen” or of the lunar highlands. This technique Going further camera on a tripod. “unsharp mask” feature of your software, or works especially well on raw and TIFF You don’t have to stop with one 5-second even the wavelet transforms provided by images. Unfortunately, JPEG compression exposure of the same scene. Take a dozen To read part one of this series, about Scorpius the Scorpion shows many more stars than appear to naked eyes in this 5-second exposure RegiStax (http://registax.astronomy.net). tends to blur these subtle colors. — M. A. C. or more and let Deep Sky Stacker or other how to choose a camera, visit www.Astronomy.com/toc. taken through a 50mm lens at f/2.8 and ISO 1600. Your first fixed-tripod astrophoto probably will astronomy software combine them in look something like this. Michael A. Covington

66 Astronomy • January 2011 www.Astronomy.com 67