Reposted from December 30, 2012
As we begin our mental preparations for Monument Valley, I'm passing a long a few thoughts and extra resources to help you prepare for shooting night landscapes with little or no moon. There are three or four primary genres of star images that we can attempt. The pre-conditions for success are:
Types of Star Images 1. Single frames images. The simplest images to make are single long-exposure frames. Long exposures are typically 10-30 seconds or more if your camera or interval timer will allow it. The limiting factor is the rotation of the earth which will impart a blur to your images above a certain amount of exposure time. The amount of time you can expose without blur is a function of the focal length of your lens. To determine the maximum exposure time before blur occurs, use the formula 650/focal length in mm = max exposure time in seconds. For instance, the max exposure time before blurring for a 24mm lens is 650/24 = 27 seconds. For a 100mm lens, the max time is just 6.5 seconds. Conversely, for a 14mm lens, the maximum time is 46 seconds. Tests by experts confirm that whatever lens used is best stopped down at least one stop from its widest aperture for better performance under the demanding conditions of astrophotography. So even if you have the luxury of using a 24mm f/1.4 lens, you'll achieve better image quality at f/2 rather than f/1.4. Further, long exposures can be enhanced by using the "long exposure noise reduction" setting on your camera. The camera will create a "dark frame" after your image - a blank frame using the same ISO and shutter speed. This dark frame contains the same hot pixels and sensor noise as the previous frame. The dark frame is subtracted from the light frame in-camera which improves image quality - at the cost of doubling exposure time. Single frames of landmarks can be silhouetted so that the foreground feature provides some shape and texture to the night. And we can experiment with light-painting the foreground using flashlights or handheld flash units. Added tip: use the mirror lockup function to eliminate camera shake from the mirror vibrating after flipping up. And don't pull on the cable release. Double-bonus tip: focus using Live View in 10X mode and focus on a bright star to ensure that the stars are sharp in the final image. 2. Star trail images. Star trail images are very long exposures - from 15 minutes to several hours. These long time exposures capture the rotation of the earth in the form of curved light trails formed by the stars in the sky against the dark backdrop. Because the earth revolves around Polaris, the North Star, star trails will appear to revolve around Polaris if it's in your frame. Trails made facing east, west or south will show a portion of the arc, but not full circles. To capture these images either take one long exposure (simple) or take a series of shorter exposures of 30-60 seconds using an interval time to automatically fire the camera and composite the series on your computer after the night is over. Using the same settings from a single frame setup, 30-120 minutes of 30 second images composited can create a spectacular night sky image. In my opinion, there is no need to use long exposure noise reduction if this is your intention as the stack of images will erase any noise in the foreground. The advantage of one long image is simplicity. Unfortunately, if a plane or planes fly through your image, you'll be stuck with the streaks from their lights running through your frame. Or if someone drives through, or if you accidentally turn on your flashlight and light the foreground you'll be stuck with the accidental light as part of your composition. If you shoot a stack of 150 images, and you have five instances of stray light, you can just toss the bad frames out of the stack and use the good files. Free Software: StarStax for Mac; Image Stacker or Deep Sky Stacker for Windows 3. Star trail images can also be the source files for a new seconds of terrific time lapse video footage. If you figure 24-30 frames per second, even three hours of imaging will only yield 5 seconds of footage, so don't get your expectations high. But it is fun to play with. This first one is straight time lapse. http://www.youtube.com/watch?v=eF-SkdTF9Nc&feature=youtu.be This next video uses the interim files from StarStax (which composites star trails) to create a more flowing look to the sky. http://www.youtube.com/watch?v=tFsV6aPKbEE&feature=youtu.be 4. Long exposure, wide-field deep space imaging - if you bring a polar equatorial mount that rotates opposite the earth's turn, you'll be able to make deep space images longer than whatever you computed in #1. Instead of 30 seconds, you can make 120 - 300 second images or even longer. I use an Astrotrac TT320X ($550, discontinued). Vixen makes the Polarie, a similar small travel mount ($650.) The Astrotrac can be used with lenses up to 300-400mm. But for this trip, it will be used mostly with wide angle and short telephoto lenses to increase the exposure time for the starfield, while leaving room in the frame for a monument or two in the foreground. With any luck, at the end of an exposure we'll be able to rim-light the monument with a couple of pops of flash for definition.
Additional thoughts: - Bring a small sheet of rubylith (flexible red plastic sheets from an art supply or hobby store) to rubber band over your flashlight. The red light will preserve your night vision and keep your eyes adjusted to the dark moonless night. - Bring warm clothing layers suitable for standing around in the cold. Long johns, down jackets, hats, gloves, warm socks and boots. And hand warmers if you have them. Night shooting involves a lot of sitting around and is much slower paced than daytime shooting. And cold saps energy, so come prepared to stay comfortably warm. - Stay flexible. We're going to have winter desert weather which can range from sunny to stormy. We have three nights available so that if one doesn't work, we don't feel too bad. Right now the long range forecast looks good but who knows?
A few more links: A book-length comprehensive guide to night star photography online. (If interested, the book-on-cd is totally worth it. I have it and love it as a reference guide.) http://www.astropix.com/HTML/I_ASTROP/TOC_AP.HTM
Some inspiration from Nightscapes master Royce Bair: http://www.flickr.com/photos/ironrodart/sets/72157627607005290/
Map of Monument Valley http://www.americansouthwest.net/utah/monument_valley/map.html
Star trails over Monument Valley http://fineartamerica.com/featured/monument-valley-star-trails-jane-rix.html See you soon!