Wednesday, January 9, 2013

How to Photograph the Milky Way

How to Photograph the Milky Way
Last week, I took a photo of the Milky Way above an old schoolhouse building in Idaho. I posted the photo on our Facebook page, and it received 1,548 likes, 177 comments, and was shared 84 times. I was pretty happy (okay, fine… I was ecstatic) that so many of you said such nice things about my picture.
MANY of you asked how the photo was taken, and wanted a tutorial on photographing the Milky Way.  Your wish is my command.
Milky Way in Idaho
Camera Settings for Night Photography of the Milky Way
Shutter speed – 30 seconds: For this photo, I shot most of the night using a 30 second shutter speed (meaning that a professional tripod is necessary to keep the camera rock solid).  I find that if you use a shutter speed that is too long, the stars in the sky start to look oblong because of Earth’s rotation.  30 seconds of shutter speed only makes the stars look BARELY oblong, and you really only notice it if you zoom way in on the computer.
However, don’t take 30 seconds as the perfect answer for taking pictures of the stars that aren’t star trails.  The longer the lens you use, the shorter the shutter speed will need to be.  If you shoot on a crop sensor camera with an 18mm lens, you probably won’t be able to use a shutter speed longer than 15 or 20 seconds, because the stars will appear larger in the frame, so the streaking is far more noticeable.
Aperture – f/2.8: Normally, you would want to use a high aperture for landscape photography to achieve maximum depth-of-field.  Photographers often get tricked into thinking they need a very high aperture since the stars are far away, but remember that depth-of-field is about how much of the picture is sharp, not where the sharpness appears.
So the correct aperture for this photo is–the lowest f-stop you have available to you on your lens.  By focusing on the stars, you’re focused to infinity (the furthest out the lens can focus), so you can use a low f-stop to capture the dim star light.
In this photo, I had a lens (the Nikon 14-24mm lens) that could go down to f/2.8, so that’s the aperture value I used to take this picture.  The trouble with using such a low aperture value is that I chose to take this picture with a large foreground element, the old schoolhouse, so when I used f/2.8, the house was blurry since I was focused on the stars.  Knowing that it would be impossible to shoot a photo in such low light with an f-stop like f/16 that would have afforded me more light, I chose to shoot one picture of the stars at f/2.8 and one picture focused on the house at f/2.8.  Then I simply combined the two in Photoshop.  If you’re a “get it right in the camera” zealot, this may not sound like an attractive way to take this photo, but I promise you that it is also the ONLY way to take this photo.  Yep, the only way.  You need a high f-stop for the depth-of-field, but a low f-stop for light gathering… so you have to use post-processing.
If you take a photo out in the woods or the desert or another open location with nothing in the foreground to worry about, then you could easily just shoot at f/2.8 and forego the Photoshop bit.  But if you’re shooting a photo just like mine, there is no other way with current technology.
ISO – 3200: Normally, photographers like to keep the ISO as low as possible to prevent the photos from becoming grainy.  However, many types of night photography require high ISO values.  Such is the case here, where I shot with an ISO of 3200.  If you have a camera made in the last couple years, it will likely allow you to choose an ISO as high as 3200 or even higher (I shot some photos this same night at ISO 6,400).
Since I shot at ISO3200, there is definitely some noise in the picture I took.  Frankly, that is unavoidable with current technology, but there are quite a few things you can do to at least mitigate the noise in the photo caused by the high ISO and long shutter speed.   One of those methods is long exposure noise reduction.
Long exposure noise reduction is available on all DSLRs (that I know of, anyway) that were made in the last few years.  On a Nikon, you’ll find “Long Exposure NR” in the shooting menu of the camera.  On Canon cameras, go to your menu, then go to custom functions, and browse through them until you find long exposure noise reduction (it’s a different custom function on each Canon model).  This feature uses a technology called dark frame subtraction that I explain in the video associated with this post.
How to Focus for Night Photography
All autofocus systems require some amount of contrast in order to find proper focus.  When shooting at night, there is rarely enough light outside for your camera to autofocus properly.  The best way to solve this problem is to look around you for a street light or other light that is the same distance away from you as where you want the focus to be.  Then, autofocus on that light, and slide the focus mode switch on your lens to “manual” this will keep the focus where you last set it as long as you don’t accidentally twist the manual focus ring at the front of your lens.
If you’re taking a picture of the stars and don’t have to worry about focusing on anything in the foreground, then you may want to rack your focus all the way out as far as it will go, and then come back just a slight bit.  This will focus your lens to infinity (as far as it focuses), which is always the proper focus for shooting the stars.  If the moon is bright enough, you could also focus on the moon and then you’re set.
If I need to focus on something closer to the camera, like how I focused on the schoolhouse for one of the photos, then shining a bright flashlight or laser pointer on the building will help your camera to find focus.  One other technique is to simply show up to the location where you’ll be shooting before it’s actually night time.  Then you can adjust your composition before it gets dark, and lock down your focus while there is still enough available light.

How to See the Milky Way
Most people never see the Milky Way with their naked eye.  Usually, the artificial lights from houses and streetlights are too bright for our eyes to see the faint glow of the ring around the Milky Way at night.  However, by using the amazing light gathering ability of newer DSLRs, the Milky Way can usually be captured in a picture.
I intentionally waited to take this picture until a night that did not have a bright moon.  This lessens the amount of light in the sky to make the Milky Way less visible.  Also, I drove 1.5 hours away from the nearest major city to get rid of all of the city lights.  In this rural location, I could see the Milky Way with my naked eye, which was intensified when I took a picture and gathered the light with a 30 second exposure.
Frankly, I’m not much of an astronomer to tell you if the Milky Way is visible, or even to point you to a resource where you might find out when and where the Milky Way will be visible.  But in Idaho, I find that it’s visible most all of the year for most of the night.  I just go out and shoot a couple times to know where it will rise and set, and approximately what time of night.  For this shoot, I knew the Milky Way became visible as soon as it was FULLY black outside, and was directly overhead around 2PM.  Perhaps someone in the comments can point us to a good resource to check the sunrise time/location for different parts of the world.
Photos like this don’t happen by accident.  It takes a lot of practice and planning to take a photo of the Milky Way, but the payoff is huge!  Although it was quite cold outside taking this picture since I didn’t bring a proper jacket, the time I got to spend out in the middle of nowhere looking at the brilliant stars for a few hours last week was incredibly soothing.  Not to editorialize too much, but seeing the galaxies and stars and planets so far away, it made me laugh at the thought that a big bang could have caused it all.