Celestial Photography

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The moon and the stars have always held a great amount of fascination for us humble inhabitants here on Earth. Since the invention of the camera, photographers have striven to capture the brilliance of the night sky. At one point or another we’ve all hauled our tripods out to the back yard in the middle of the night. Here are a few tips to keep in mind.

Stars:

A lens with a wide aperture is key in capturing the dim light coming from the stars. Using a wide aperture allows for a shorter exposure time to reduce the noise in the picture, but it also results in a shallower depth of field. In order to strike a balance, start with f/5.6 and work from there. If you don’t happen to have a high-zoom lenses, a medium range of around 80mm also works well.

Get familiar with some of your camera’s more advanced settings. One is “mirror lockup”, which locks the camera’s internal mirror in the “up” position for a moment before the shutter fires, to reduce camera vibration and increase image sharpness. Also, become familiar with your camera’s timer function, or use a remote shutter release. Long exposure will result in fascinating star “trails” as the image captures the revolution of the Earth under the stars. The longer the exposure, the longer the trails. Shorter exposure (about fifteen seconds and under) will show static stars with little evidence of trails.

For very long exposure (an hour or more) to capture very long star trails, be sure your camera’s battery is fully charged, or is hooked up to an external power source if it has that capability. Use your camera’s “bulb” setting, which keeps the shutter open for as long as the shutter release button remains depressed (or in many digital cameras, pressing the shutter once begins the shot, and pressing it again closes the shutter) and gives the photographer complete control over the length of exposure.

Choose a time when the sky is clear – exposure times will differ depending on how much light the moon is casting (less exposure time for a full moon, more for a new moon). Air traffic is greatly reduced between midnight and 3:00 a.m., so keep that in mind in order to keep your photograph clear of airplane trails (though sometimes they add an interesting element to the shot). Set your camera up on a tripod, compose the shot, and set the focus to “infinity”. Start with a low ISO, but if you’re not satisfied with the image quality you can increase the ISO by increments until you achieve the look you want.

Moon:

To photograph the moon well, a telephoto lens is key in order to bring the moon “closer” to fill the frame, and capture the details on the surface. The use of a 2x converter on a non-telephoto lens also works well to enlarge the moon. Because the moon is the light source and is brighter than you might think, start with an ISO of 100. The “rule of thumb” is an aperture of about f/11 (the higher the aperture, the less sharp the image), and exposure at 1/125. Start from there and fiddle around with the settings for your specific circumstances. Set your camera to manual focus, since auto focus sometimes gets confused on moon shots.

You might actually require less exposure than you’d think. Somewhat UNDERexposing a shot will allow you to amp up (or, down) the contrast and curves during post-processing, which will bring forth crater detail. Longer exposures result in movement blur as the moon “moves” across the night sky, so try to keep exposure under 1/15 of a second.

Add some variety to your moon photography by shooting the various phases. The side-lighting that occurs during the moon’s phases can add a dramatic effect your images. A longer exposure will probably be required than what would be used during a full moon because a half or quarter-moon throws less light than a full moon. Photographing the moon at various stages in the night sky offers another dimension – a moon closer to the horizon appears “larger” to the naked eye, and therefore to your camera’s lens, due to the magnification effect of the atmosphere combined with the curve of the Earth. Shooting earlier in the evening or closer to dawn also produces interesting lighting effects in the horizon.

Above all, practice is the key to success when photographing the night sky. Fiddle with settings, exposures, and composition until you find a combination that works for your conditions. It might make for a late night or two (or three), but the end result can be extremely rewarding.

For more information on photographing and focusing in the dark, check out this article.

Photo Credits (in order of appearance):
- “HowTo: Startrail” by Johan J.Ingles-Le Nobel on Flickr Creative Commons.
- “Bad Moon Rising” by make less noise on Flickr Creative Commons.

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  • http://danflanphoto.com Daniel

    Great tips. But the moon is actually no different in appearance, at least size wise, regardless of its position in our sky. In fact, atmospheric refraction will actually decrease its angular diameter by up to two percent when near the horizon; the moon just looks larger when because out minds perceive things on the horizon to be closer than things in the sky.

    You can also do wide field imaging (no trails) using nothing more than your camera and something called a barn door mount. Using this method I have been able to photograph star clusters and capture, say, 1,500 stars in a single image, none of which are visible to the naked eye. This is across a field of roughly six degrees (our moon is a half a degree).

    We use the term apparent magnitude to measure the brightness of celestial objects. The higher the number, the dimmer the subject…the naked eye can see up to about a 6.0. The sun is -25 and the moon -12. Using the aforementioned methods and shooting at 300mm, f/2.8, I have been able to capture up to about a positive 14 for a 60 second exposure. Amazing stuff when you think about it. The Pleiades makes a great subject because you actually pick up colorful nebulosity when doing exposures of ten minutes or more. Just keep in mind that anything of this length needs to be tracked to avoid trails, be it via the barn door method or on an actual scope.

    Another tip when shooting tracked, especially when the mount is polar aligned with extreme precision, is to take multiple exposures and stack them in Photoshop. This produces a higher signal to noise ratio since the stars are the constant and the noise is different in every frame. Stacking four decreases noise by a factor of two, sixteen by a factor or four, etc. Some of the most beautiful deep sky photographs are often stacks of, say, 300, five minute exposures.

    Overall astrophotography is a lot of fun and one needs nothing more than a low end DSLR, remote release or timer, tripod and patience. A barn door mount is inexpensive and very precise for exposures under a few minutes. And on the extreme end we can mount a camera body on a scope and photograph deep sky objects, but that is a topic for another time. Happy shooting!

  • http://twitter.com/Snerkology Tiffany

    Wow, Daniel, what great information! You're obviously very knowledgeable on the subject. Thanks so much for sharing with us!

  • http://www.flickr.com/photos/43147325@N08/ Johan J Ingles-Le Nobel

    I'd like to echo that: Dan's tips are most excellent. In fact I made the top of the two images that you've used to illustrate your article with stacked images and free software called “startrails.exe”.

    There are some additional tips for people if you click through on the image – this really is a lot of fun!

    Johan J Ingles-Le Nobel

  • http://twitter.com/Snerkology Tiffany

    Johan, you did an excellent job, thank you so much for making your images available via Creative Commons! I read your tutorial and found it to be very informative.