Photographing the Milky Way
Photographing the stars or the Milky Way at night can be a little tricky. And, unlike most other areas of photography, whether it be landscapes or portraits, the equipment makes all the difference in the world. Good results come with a hefty price tag.
When photographing at night, light from the stars is as good as gold, and you want as much of it as possible. You accomplish this in two ways. The first being a good camera body and the second being a "fast" wide-angle lens.
A full-frame camera body has a larger photo-sensor that's able to capture a little more light than an APS-C crop sensor camera. The second advantage of a full-frame body is that it has a 1.0x multiplier when paired with a lens. A crop sensor camera usually has around a 1.6x multiplier. So, for example, a 16mm lens on a full-frame body is truly 16mm. On a crop-sensor body, the 16mm lens is really a 24mm lens.
The lens is perhaps more important than the body. When shooting the Milky Way, you want a wide angle lens. I prefer anything from around 14mm to 24mm. This allows for a very large Field of View (FOV) so you can capture as much of the night sky as possible. The crop-sensor camera makes finding a large FOV lens difficult because of the 1.6x multiplier.
You also want a very fast lens which will let in a ton of light. The lower the f-stop number (or the larger the aperture), the better. A lens with an f-stop of 2.8 is good. But a lens with a 1.4 aperture would allow in 2x as much light as a 2.8 aperture. Another way of thinking about it is, the 1.4 lens would cut the exposure time in half as compared to the 2.8 lens given the same amount of light. And exposure times are important. After about 25 seconds, the stars will no longer appear as small round dots. They will start to smear and look more oblong in shape. Therefore, the shorter the exposure time, the better, provided you can capture enough light.
Another way to shorten the exposure time is to increase the ISO setting on the camera. When increasing ISO, most cameras start to produce noise. Some of the newer full-frame bodies are ISO-invariant, meaning increasing the ISO setting introduces no additional noise than had a lower setting been used. This is ideal, but also comes at a hefty price.
When shooting the Milky Way, you need to operate around ISO 1600-6400, and most crop-sensor cameras are going to have a lot of noise in that range. Even the lower end full-frame bodies will have noise, but it’s manageable in post-processing. However, a lot of the newer camera bodies handle noise much better than even just a few years ago.
Lastly, you’ll need a nice sturdy tripod and a cable release, or remote trigger capability. Exposure times will vary, but keep in mind, anything longer than about 25 seconds is going to capture the Earth’s rotation and smear the stars.
Regardless of body and lens, focusing can be tricky. Auto-focus will not work at night, no matter what camera body you use. And rotating your lens to “infinity” won’t work either. The lens can actually focus beyond infinity such that nothing is in focus. You have a couple options.
The first is, go into Live View if your camera supports it, point the camera at a bright star or planet, crank up the ISO to a really high setting so your camera can see it, and rotate the manual focus to get the star to look as sharp as possible. If you have a Canon camera, while in Live View mode you can press the magnifying glass button twice to zoom 10x. This makes focusing easier.
The second option is to take a picture, view it, zoom in as far as you can and see if the stars are in focus. Make an adjustment by rotating the manual focus ring on the lens either clockwise or counter-clockwise, take another shot, and compare it to the first shot. This method involves a lot of trial and error.
Here were the camera settings for the photograph shown at the beginning of this blog entry: It was taken with a Canon 6D using a 16-35mm f/2.8L USM II lens. It was a single exposure. The settings were f/2.8 at 16mm with a ISO 6400 and a 17s exposure time. The clouds low on the horizon were light up orange by the small towns about 50 miles away. I used a flashlight to “paint” the old abandoned house and foreground during the exposure. I also did quite a bit of post-processing in Adobe Lightroom.