Star Photography 101

This is intended to be a quick guide to shooting astrophotography / star trails / night photography.

What do you need to take your night photograph? There are alternatives to some of these tools, as my list is not the all-inclusive list (there are no rules to art). However, these are the things that I find are mandatory to produce my stars images.

1. A tripod
2. A lens with a manual focus function that shows you where infinity is (I primarily use the Canon EF 17-40 L lens)
3. A remote or intervalometer
4. Fully-charged batteries and at least 4 GB of memory (or at least a roll of film)
5. A lens hood is a good idea but not mandatory

First off, you need to decide whether you want to shoot star trails or stagnant stars. Stagnant stars are brightest during a new moon or when the moon has not risen, but it is possible to photograph them (the few that show up) in lit areas. The photograph below was taken before moon rise. It is a 13 second exposure at f/4.0 ISO 1600. The light is from the environment (ie no light has been added).

An oil rig in Coalinga, California - (c) 2012 J. Rae Chipera all rights reserved. Licensing for use of this photo is available on my webpage.

How long can you have your shutter open without the stars moving? The best way to calculate this is by using the rule of 600. It's a math problem, but it's important. If you take your lens focal length and divide it into 600 you will know the exact amount of time it can be open before the stars blur. If you are using 35mm, you would divide 600 by 35. 600/35=17.14 so you have roughly 17 seconds before the stars begin to blur.

If your camera has a crop sensor, you need to take that into account. For example, the image above was taken with my Canon 50D which has a crop sensor, so my 17mm with the crop sensor turns into about 24mm. That makes the equation into 600/24 instead of 600/17.

Next you must determine whether you want to shoot a silhouetted image with the stars or if you want the rest of the image visible and lit.

1. If you plan to shoot silhouettes, you will probably have best results during a new moon or when the moon has not risen yet. 
2. If you plan to shoot with a nicely-lit foreground or subject you are better off shooting when there is a risen quarter moon or full moon. Not only will this light your ground, but it will also create shadows. Of course, this can also be accomplished also by non-natural lighting techniques - headlights, building lights, flash lights, etc.

Next, you have to decide which direction to face in order to make your composition turn out the way you want. Sometimes you have no choice, but other times you can choose where to place your camera in relation to the stars and the subject.

"Reminiscing Rhyolite" - (c) 2011 J. Rae Chipera all rights reserved. Rights to use of this photograph are available on my website. Photograph taken at Death Valley National Park.

Pointing the camera lens north will give you a nice circle in the sky around Polaris, the north star. This is a cool effect that seems to be the most-popular. The image above is a 45-minute exposure at f5.6 and ISO 320 facing north.

Image credit: Ethan Siegel science blogs.com "Stars with a Bang":  http://scienceblogs.com/startswithabang/2011/04/telescope_give_me_sight_beyond.php   

To find Polaris, locate the Big Dipper (the big soup ladle) and then follow the line created by the two ladle stars furthest from the handle to the next star. You can remember which way to go because you move in the same direction as the slight bend in the handle. This star is part of the less-obvious little dipper and is Polaris, or the north star. 

Pointing the camera east or west, depending on the latitude at which you live, will give you a sideways arc in the sky or a diagonal line of stars across the sky. The image below is a 45-minute exposure at f4.0 and ISO 200 facing east.

"Martian Colony" - (c) 2011 J. Rae Chipera all rights reserved. Licensing for use is available on my website. Photograph taken in Cuyamaca, California. 

Pointing the camera south will give you an arc across the sky. The image below is a 1 hour exposure at f4.0 and ISO 400 facing almost straight south.

"Badlands on the Green Planet" (c) 2012 J. Rae Chipera all rights reserved. Photograph taken at Anza Borrego Desert State Park.

So now that you know which direction you want to point, how about we talk about camera settings. As far as what settings to use, there is no one way to shoot any photograph, but I typically shoot star trails as multiple 30-second (or whatever the longest setting on your camera is before bulb) exposures one-after-another. To do it this way, your camera needs a repetition mode, and you need a remote that locks in the pressed position. 

I shoot it this way with a digital camera because, unlike a film camera, an exposure longer than your longest setting can create hot pixels (little colored dots that are not part of the photo IE heated dust) - increasingly easily the longer you have the shutter open. So if I am going to have my shutter open for an especially long time (like say, a half an hour) I do it this way to mitigate that.

I then use a computer program to merge them into one file. So far my favorite is also the cheapest - I use ImageStacker, which is written in Command Prompt (so if you have a PC you're good to use it.) It cost me $17 to download. I then select "merge to brightest pixel" and then I get the same image I would have ended up with had I left the shutter open the whole time.

How do you get the focus / aperture / exposure correct? Well you want to put your lens on manual focus and set it to infinity (because that's how far away the stars are... right?) and then use your light meter to find an exposure that is good for 30 seconds (take some test shots). I typically tend to shoot my images a stop or two too dark, but that's a matter of personal preference.

If your camera does in-camera noise reduction immediately after the image instead of after the set, you don't want to use it on repetitive images star trails because you'll end up with gaps between the stars. If you are worried about a noisy image, I would suggest trying to shoot with the lowest ISO possible - ie wide open aperture and longest shutter speed to go with that idea. If you still have an image that is too noisy, I fear there is no way to reduce that without more nifty computer software. I recommend Adobe Lightroom, but there are other options available as well.

I hope this helps to answer some questions about photography at night. Feel free to leave any questions in the comments.