I am not an astronomer. I am not a professional photographer. I’m a guy who owns a camera.
A health issue got in the way of this trip so I was not able, yet, to put any of this into practice. I’m saving it, though, because I’ll get there soon enough. Also, most of this is old news– I’ve changed equipment and technology has advanced. I’m hoping to revisit the project and get out in the dark later this year (2017).
While planning a driving trip to Zion National Park, I ran across the Dark Sky Finder, a utility that maps light pollution (and the lack of it) across the U.S.. According to that map, our drive to Zion would take us through areas that have very little light pollution– indeed, the Finder showed that for a part of our drive we’d skirt an area in Utah that was “extremely dark with no noticeable light pollution.” This meant, of course, that we could see stars– lots and lots of stars. I’m not an astronomer, but my wife and I do appreciate a beautiful night sky (who doesn’t?), and I do like to play around with cameras (night sky photography, perhaps?). So this piqued my interest.
In a nice, dark spot on the map, I found the rather evocatively named Goblin Valley State Park. There’s a small campground in the park, which was perfect– we could do our sky gawking and picture taking just a walk from our tent, rather than take a cumbersome car ride back and forth from a distant (and light polluting) hotel. I booked a campsite. We would have one night.
A little further research turned up the Goblin Valley State Park Light Pollution Map which described the brightness of the stars in the night sky at Goblin Valley thusly: “Zodiacal light annoyingly bright. Rising milkyway confuses some into thinking it’s dawn.” I was getting more excited about this leg of our trip, and thought: the Milky Way? I could see and take a picture of the Milky Way?
It turns out, according to the Internets, that taking a photo of the Milky Way is not that hard if you (1) have a mid- to high-end digital camera and an appropriate lens, and (2) are willing to do a little work. And, of course, if you manage to be in the right place at the right time.
It certainly looked like we would be in the right place at the right time. Goblin Valley gets about as dark as it gets in the lower 48. We’d be there on a night when the moon, which would be only 7% full anyway, sets early (leaving only starshine in the night sky). All we’d have to worry about is the weather (and perhaps atmospheric pollution), which we could keep an eye on using the Goblin Valley State Park Clear Sky Chart.
But what about the camera and the work?
For night sky photography, a camera must be in full manual mode; none of the auto modes will give anything near acceptable results. According to the various sites I consulted, the proper exposure for the Milky Way on a moonless night is 30 seconds at f/2.8, ISO 6400. Or, 30 seconds at f/2.8, ISO 3200. Or, 90 seconds, f/2.8, ISO 3200. Obviously, this was going to be a matter of trial and error.
There was one constant piece of advice throughout the star photography sites, though. The stars move across the sky, and if the camera shutter is open too long the movement of the stars will smear the picture. (This is an attractive thing for some night sky photographers, but not for me. I wanted the stars to look like stars.) Almost all of the online gurus offered the “500 Rule” to prevent this smearing. That is, the longest shutter speed you can use (in seconds) before the stars start to show trails (i.e., smear) is: 500 divided by the 35mm focal length of the lens you’re using. This is completely independent of f stop and ISO speed. For example, if I have a full frame camera with a 10.5mm wide angle lens, the longest shutter speed I can use for star photography is about 48 seconds [500/10.5]. If I use the same lens with a camera that has an APS-C (1.5 crop) sensor, the maximum shutter speed drops to about 32 seconds [500/(10.5 x 1.5)]. A few sites were more conservative and suggested using a “400 Rule” instead.
Obviously, the “500 (or 400) Rule” means that the shorter the focal length, the longer the exposure and more light reaches the sensor, all other things being equal. But all things aren’t equal in my camera bag. The cameras I own that are appropriate for this work are APS-C (crop) sensor cameras, and the lenses I have that might be appropriate for this task are: (1) a 10.5mm f/2.8 fisheye; (2) a 17-55mm f/2.8; and (3) a 24mm f/1.8. I was determined not to buy any new equipment for this shoot (harder to resist than it sounds). It seemed a no-brainer to go with the 10.5mm, until I realized that a 32 second exposure at f/2.8 with the 10.5mm lens allows slightly less light to reach the sensor than a 14 second exposure at f/1.8 with the 24mm lens. (How Many Stops? was very helpful in determining this.) Add to that the fact that the 24mm lens doesn’t have the fisheye distortion of the 10.5mm, and my equipment choice was made: the 24mm f/1.8, mounted on my Sony NEX-7.
*OK, I cheated here and bought the Eye-Fi card for this shoot. Since the camera settings were very much a trial and error thing, I wanted to be able to examine the pictures as they were shot, without disturbing the camera. The ad-hoc network this card establishes with my iPad does the trick– I take a shot, and the jpg version is immediately transferred to my tablet. I’ve read that some people have had problems getting this to work; I had none.
I can’t compare this to other tablets, because I’ve never used another tablet. But I found my iPad nearly indispensable. The app Star Walk told me what the sky would look like at night in Utah a month down the road. It also allowed me visualize, using a live-view, augmented reality camera during the day in Goblin Valley, where the Milky Way would appear at night. This helped a lot in selecting spots (with an eye for rock formation silhouettes) to shoot from. A GPS mapping app (MotionX GPS HD) allowed me to set likely spots for night photography during the day, and find them later at night. DSLR.Bot turned the iPad into an IR camera remote, meaning I didn’t have to carry a separate shutter release remote (that I could/would lose in the dark). The Eye-Fi app and Eye-Fi Pro X2 SD card allowed me to review shots without disturbing the camera. A simple app for calculating DoF (aptly named Simple DoF Calculator) helped a lot– for daytime shots as well as for setting up foreground objects in the night shots.
Since the 10.5mm f/2.8 was so close to the 24mm f/1.8 using the “500 Rule,” I thought I’d bring it along and give it a try if there was time after shooting with the Sony. After all, I’ll have all night!
*Sofortbild is a really nice (and free!) piece of software for OS X that allows me to completely control the D300 from the MacBook Air, and immediately download shots for review. I can change the camera’s ISO setting, aperture and shutter speed via cable– I wish there were something similar for the Sony.
I forget things, even (perhaps especially) obvious things. To help prevent me from making (probably unavoidable) mistakes, I put together a pre-shoot checklist for my camera settings. It is:
Neither of my setups– the NEX-7 with the 24mm f/1.8 lens, nor the D300 with the 17mm-55mm f/2.8 lens– have image stabilization, so there was nothing to turn off for the long exposure, tripod mounted shots.