Note: This is just a quick tutorial on astrophotography. For other astronomy resources, take a look at this collection I’ve been compiling. (And let me know if there’s something more that you are looking for.)

Disclaimer: I’m not an astrophotography expert. I just get the basic idea and I like to mess around with this. I think that astrophotography is easier than working a telescope and in many ways it’s more immediately rewarding. It also gives you something fun to play around with on even modest cameras. As long as you can keep a shutter open for a few seconds, you can do astrophotography.

You can read my basic description below. In addition:

• You’re welcome to pull up this Astrophotography Presentation that I use for workshops.
• Here’s a collection of photos taken by people at one of these workshops.
• There are plenty of other tutorials like this that are more detailed than what I’m providing here.
• Many of us carry phones around not for calling people but for taking pictures. They aren’t ideal for astrophotography because they have small sensors and apertures, but there are some apps that can add multiple exposures together. Here’s one example that I’d like to play with more.

Here’s the basic idea. The stars are very dim from our perspective, since we’re really far away from them and their light is spreading out and sharing that energy all over space, limiting us to only a small fraction of that. In addition, the amount of light collected by your pupils is really small, both because the opening collecting the light is really narrow and because your eye sensors are refreshing what they’re detecting several times per second. Also, your detection system, the retina with its cones and rods, has a limited sensitivity. With a camera, you can adjust these factors. The display on my camera looks something like this for a “normal” photo:

And, it would look something like this for astrophotography:

There are adjustments that can be made for the amount of time that the shutter stays open, and for stars I generally want to adjust this to something like 5 seconds to start, depending on the camera and the conditions. Most of the time that you take a photo in daylight, the shutter stays open for a fraction of a second. Also, I should open up the aperture as wide as possible in most cases. In camera-speak, this means you should make the f-stop be a number that is as small as possible. And, I probably want to play with the sensitivity of the camera’s detector, what’s known as the ISO. (Back in the old days, we used film that we’d say was a certain “speed,” but that was really a measure of the sensitivity of the chemicals in the film.) This is tricky because as you increase the sensitivity, you also allow for a grainier and perhaps even noisy looking background, which is exactly the opposite of what you want in astrophotography. Also, the measure of ISO is something that seems to change with each generation of cameras, and using really high sensitivities on a camera made in the last couple of years would have been unheard of just a few years previous. So, start with something and see how it turns out. For me, I have a 35mm lens (fixed focal length) that I can open up to f-1.8, and to start I’ll open the shutter for 5 seconds and use an ISO of 1600. (I use a Nikon D5300, in case that’s relevant to you.) After that I’ll just play around. If there’s a lot of light pollution, this will be way too long and the photo will be washed out. If I have dark skies, this will show wide variety of stars with a still dark background.

There are a few other important pieces. First, if you’re going to leave the shutter open for several seconds, you need the camera to be absolutely still. A sturdy tripod is important for this … or so everyone says. Honestly, I’ve used a bag of marshmallows propped on a rock with a smaller camera positioned just so, but on the other hand I’m not getting award winning images with that technique (unless it’s in a special marshmallow-propped category). Use what you have and see how it goes. But, probably the most violent time for the camera is when you’re pushing the button to take the photo. So, especially if you don’t have a good tripod, try a setting that makes the camera trip the shutter a few seconds after you’ve pushed the button, or perhaps use some kind of remote shutter button. (More and more often, there are ways to connect your phone to a camera over bluetooth or wifi.) You’ll find these options on most cameras under some menu that gives you choices for delayed shots like this, as well as for rapid-fire exposures. Finally, you need to focus on the stars. It seems like this should be easy, but I see mixed results with every camera I’ve played with. Stars are practically an infinite distance away, so you should set your focus, manually, to infinity. (Autofocus probably won’t work because there’s so little for the camera to “see.”) This always seems to be just a touch off for me, so my suggestion is to play around with it. Most of the time I use the viewfinder while pointing at a distant object on the horizon and get it as sharply focused as possible and then just leave the focus there. Stars that are in focus will look like sharp points. They shouldn’t have any significant diameter to them (unless they’re planets). Depending on your camera, you may find other focusing strategies as well. Some cameras have a digital control of the manual focus, and you can actually select “infinity” on the focus control screen.

I’ve compiled a few modest photos with a compact camera, but here’s one that I think is a good example of what you can do with a simple point-and-shoot camera (before I had a DSLR):

This is one of those photos that was taken from the hood of my car with a table-top tripod. With this photo, you can clearly make out the Big Dipper (centered, bottom third of the frame) and the double star in the handle. Above that you can make out the entirety of the Little Dipper, something that’s hard to do with the naked eye except with the darkest skies. And, at the bottom of the photo you can see a streak of fire-like light. This is actually the tail lights of a car going by, which gives you a sense of the exposure time for this photo.

Here’s a very similar field of view, but taken from a darker location in the Uintas. If your monitor if bright enough, you can make out the outline of trees that block the stars behind.

And finally, here’s a photo taken during a workshop with local teachers. This tripod was set right here on the observatory roof of Tracy Hall Science Center at Weber State. Looking north, we were able to pick up Cassiopeia, a streak from a satellite, countless other stars, and even the Andromeda Galaxy. The light from the latter is 2 million years old! (You can find a full resolution file in the original gallery.)