Date: October 28, 2011
Title: Introduction to Astrophotography
Podcaster: Adam Pender
Links: www.adampenderphotography.com and http://www.adampenderphotography.com/Nature/Astrophotography
Description: This podcast discusses equipment and techniques for taking pictures of star trails, constellations, Aurora Borealis, sunspots, the Moon, the Milky Way, and other starry night photos. Tips are provided in the podcast, and examples and settings are available to view at http://www.adampenderphotography.com/Nature/Astrophotography
Bio: Adam Pender is a rocket propulsion engineer and a NASA JPL Solar System Ambassador. He has worked on several NASA missions, including Phoenix, Juno, GRAIL, Mars Science Laboratory, and MAVEN. In his free time, he is an exhibiting fine art photographer who is especially interested in photographing the night sky.
Sponsor:This episode of “365 Days of Astronomy” has been sponsored anonymously.
Transcript:
Hello, and welcome to the 365 days of astronomy podcast.
My name is Adam Pender. I am a propulsion engineer who has worked on several NASA missions, including GRAIL, Juno, and MSL. Additionally, I am an avid photographer, which brings us to today’s topic: astronomy that you can do without a telescope: in this case, using a camera for astrophotography.
What is astrophotography? It’s an all-encompassing term for taking pictures of the night sky. This can include extremely sophisticated shots, such as those of deep sky objects using stacked exposures and motorized tracking mounts, but astrophotography can also include more traditional and simple photography techniques, using standard photography equipment.
Let’s talk equipment for a minute. Obviously, the first thing you need is a camera. While it is possible to use a simple point and shoot camera, it’s much easier if your camera has some capability to adjust settings such as aperture and shutter speed, as well as ISO, which is the light sensitivity of your camera’s sensor or film.
Along with a camera, if you’re using an SLR, you might also consider a large-aperture lens, which lets in more light than a standard zoom lens. Many SLR systems have options for lenses with apertures of f/1.4 or faster, which can add some interesting night sky observation options. As you’ll see, specialized lenses are not necessary, though.
While the camera is necessary, it will be useless without some method of supporting it, since most nighttime photos require shutter speeds of several seconds at a minimum, and which can sometimes stretch to several hours. Generally, this means a tripod, although other improvised methods of support, such as beanbags can be used in a pinch. You just want to be sure that the camera is steady.
Lastly, a remote shutter release can be helpful to take exposures longer than 30 seconds when in “bulb” mode, and also helps to reduce camera shake when pressing the shutter button. If you don’t have a remote shutter release, using the camera’s self-timer can help reduce camera shake when pressing the shutter button.
But enough about equipment, let’s talk about what you can do with it. On my website, I have posted several examples of the types of photos I’ll be discussing. You can see these photos at www.adampenderphotography.com by clicking on the galleries link, and selecting the astrophotography gallery. Under each photo you’ll see the settings used, including focal length, ISO, aperture, and shutter speed, in order to give you an idea on where to start for the different kinds of pictures we’ll discuss.
Often times, the best settings are figured out by trial and error, since most night scenes are too dark for your camera to accurately meter. For this reason, the manual exposure mode is helpful. Just remember that for a given scene, ISO, shutter speed, and aperture work together to collect the correct amount of light. If your first attempt is too dark, try increasing ISO, reducing shutter speed, or choosing a wider aperture.
The first type of night sky picture I’ll talk about is the “star trail” shot. This shot takes advantage of the earth’s rotation to turn the points of light from stars into arcs of light, over the course of many minutes or hours. This kind of shot can be accomplished in a single exposure, or if you are “photoshop-savvy” by stacking many shorter exposures to create the same effect. There are two examples of this shot on my astrophotography page: one at 64 minutes of exposure, and one at over two hours. You can see that the longer the exposure, the longer the star trails. In the 64-minute shot, I have Polaris, the North Star, in the frame, and you can see the other stars circling around it. The farther away from Polaris, the longer the apparent arc of each star, in the Northern Hemisphere, at least. Keep in mind that star trail shots are relatively forgiving of equipment, too. You don’t need to shoot at high ISO’s or wide apertures-you just need a way to keep the shutter open for a while with a stable camera. Also, if you can get some ground context in the frame, you can really emphasize the star motion in comparison to the “static” foreground.
One of the star trails photos also includes Aurora Borealis, or the Northern Lights. This is a great time to be getting into astrophotography, since we are approaching a solar maximum in 2013, and this extra solar activity means more chances to see the Northern Lights. In fact, by taking long exposures with a camera, you can see the northern lights more clearly than you can with the naked eye, especially if they are only faintly visible. Don’t worry if there are a few clouds in the sky either-the interplay between patchy clouds and northern lights can make for some very interesting night sky photos, as you
can see from the other examples on the website.
Speaking of solar activity, it’s also possible to directly photograph sunspot activity during the day. This requires a longer telephoto lens, as well as a Mylar “solar filter” to reduce the light that the camera sees, in order to avoid damaging the camera and your eyes.
With a long telephoto lens, it’s also possible to take detailed shots of the moon at night. Just remember that when the moon is visible it is in direct sunlight, so you’ll need to adjust exposure to compensate for how brightly lit the moon is, compared to the surrounding dark sky. This will help you avoid a moon shot that looks like a detail-less white circle. The easiest way to do this is with manual exposure, using the “sunny 16” rule as a starting point. Remember that the moon is traveling across the sky, and with longer focal lengths and higher magnifications you will need higher shutter speeds to freeze this motion and capture maximum detail. Also, while the full moon might be most impressive to the naked eye, a slightly less full gibbous moon can have more texture and look more “3-D” due to the direction of incident light. It definitely pays to experiment with different settings, and try to take these pictures during different moon phases.
Back to stars, there are lots of opportunities to get great photos of starry skies. With a reasonable combination of equipment and settings, it’s possible to get great images of constellations. On my site, there are examples of the Big Dipper, Orion and the Pleiades. These photos were taken with 30 second shutter speeds and wide angle lenses. At 30 seconds, the amount of star trailing is relatively small, and the stars still appear as distinct points. As you’ll notice, these starry sky photos show more stars than are typically visible with the naked eye. This is a great way to see dim stars and constellations, but picking out constellations among the jumble of stars can be difficult. In the big dipper photo on my site, the brightest stars which make up the big dipper are also reflected in the calm water of the lake, which helps to accentuate the constellation.
You don’t need to have a specific constellation in mind to take compelling wide field star pictures. You can also take photos of familiar scenes at night, and include starry skies above for a new look. The photo of Half Dome in Yosemite National Park takes advantage of a setting moon to illuminate the ground, with the dark sky to the east full of stars, and with a few airplanes showing up as flashing streaks through the sky.
It is also possible to use the same approach to take pictures of meteor showers, although there is a bit of luck involved: you need to have the shutter open before you see the meteor in order to capture it. Fortunately, digital cameras let you hundreds of photos at little incremental cost, so this is not usually a big deal. Continuously shooting 30 second frames during meteor showers will often result in catching at least a few meteors. The meteor photo on my site was taken on Mt Baldy, near Los Angeles, during the Geminid meteor shower. The meteor is visible as a streak on the right side of the photo, just above the trees.
You can also make the Milky Way the primary subject. Using a fast-aperture lens, high ISO, and a relatively fast shutter speed to prevent any star trailing and retain detail and sharpness, it is possible to get detailed images that show the structure and color of the galaxy in a lot of depth. The photos shown on my website were taken at Independence Pass, near Aspen, Colorado. This is a great location for Milky Way shots for two reasons: First, it is far away from major cities, so light pollution is less of an issue. Second, it is at high altitude, in this case more than 12,000 feet above sea level. This means there is less air to reflect any stray light. These shots also benefit from being taken during a new moon, so there was no glare from the moonlight to reduce contrast in the galaxy. Of course, it is possible to get good results at sea level as well-just keep experimenting.
In all cases when it is dark out, focusing can be a challenge. Try to find a bright star or the moon to manually focus on, then recompose for your shot. With astrophotography, the biggest thing is to get outside and enjoy the night sky. Experiment with your equipment and techniques-trial and error is often the best teacher.
I hope you enjoyed this discussion on astrophotography, and that it has inspired you to get outside and try to take your own night-sky pictures. I’m Adam Pender-thanks for joining me.
End of podcast:
365 Days of Astronomy
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