Guest post by Justin McKee
Alright, enough boring stuff. For the past few weeks my guest posts have discussed a lot of technical mumbo jumbo and I think it’s time I changed that.
This post is about long exposures.
A long exposure is when you have your camera (preferably a DSLR) set up on a tripod with the shutter speed adjusted for a time that is longer than a second (roughly).
What’s the practical application?
Well, you can take pictures of the night sky, cars passing by or very dimly lit environments and they won’t look supremely noisy because your ISO won’t be cranked. The long exposure time allows more light to come into your camera, which means your aperture and ISO can take a break for once.
So, given that we’ve already covered the boring stuff, you should know that when you use a shutter speed that’s longer than a second, any subjects that move in your photograph are going to be blurry. Alternatively, if your camera moves, your entire picture will be blurry (hence the tripod for maximum stillness).
When shooting long exposures you won’t be shooting subjects that are moving too much. The only time subject movement really applies is when you’re taking photographs of the stars or storms — but that’s just artsy and cool, so it’s OK.
If you do choose to have a living subject in your photo, it’s important to let them know that breathing is an all right thing to do, but not much else. If you’re outdoors under the Milky Way and have a friend who wants to stand in a field with their arms stretched towards to the heavens, it would be fair to let them know that they’ll have to hold VERY still for at least 15 seconds or more.
Let’s focus on a single subject for this post regarding long exposures: Astrophotography; taking photographs of the night sky.
Whenever you choose to go out and take photographs of the stars, you’ll need to keep in mind that you’re going to be taking a picture of a moving subject. Well, to be truthful, you’re actually the one that’s moving. The earth below us is constantly in motion and exposures over a few seconds long can create a very cool effect: Star trails.
If you keep your shutter open for long a enough period, you’ll see the stars moving across the night sky. How cool is that?
When shooting astrophotography, one of your first decisions should be where you’re going to shoot. Shooting photos of the night sky in the city is a no-go. There’s too much light from the city polluting the sky for you to capture all the stars. Go out into the country for best results.
Next, it’s time to find out what kind of lens you’ll want to use. You’re going to want a lens with a wide aperture. F/2.8 or wider is best. The next decision regarding your lens is going to be what focal length you’ll want.
Do you want to take a photograph of most of the night sky or a specific star? That will depend on the focal length of your lens. 16mm will take a photo of most of the Milky Way. 300mm will let you zoom in nice and close to the moon.
One last thing about the lens: Focusing. Stars are very far away. It’s important to set your focus to that distance. Autofocus isn’t going to cut it either, so don’t try it. If your lens has a focus window … good! Just set your focus to the infinity symbol. If your lens doesn’t have that feature, try turning your camera’s live view mode on to digitally zoom into the stars in the center of the frame. Focus the lens using that nifty feature and your focus will be close to perfect.
Next, you’ll want a sturdy tripod. This is especially vital if your long exposure is going to be hours long. Any bumps or slight movements can ruin an otherwise great photograph. OK, I lied: The last thing you’ll need to do on your lens (because you’re using a tripod) is to turn of any Image Stabilization/Vibration Control/Optical Stabilization. We’ll cover that more in a later post. For now, just trust me.
Alrighty, enough hardware stuff. What is your photograph going to look like in the end? Well, it’s important to get two things right when composing your photograph. You’ll need to make sure that the horizon is level. Shooting a test shot with a high ISO and quicker shutter speed is a good way to check that. Next, you’ll want to find a good foreground subject so your photograph isn’t JUST stars.
I mean, you can do that if you want — but having a foreground subject can really create some nice visual interest other than the stars.
Setting up your camera depends entirely on what kind of photograph you want to take. Do you want to take a photo with the stars in motion or still? Either option requires different settings.
Your shutter speed, aperture and ISO will need to be very specific to capture star trails properly.
First, you’ll want your shutter speed to be longer than 15 minutes.
That’s right. Minutes.
That amount of time — at least to me — is a minimum to capture star trails. The trails will be too short otherwise. Use a remote shutter and your camera’s bulb mode (check your manual) to leave your shutter open for that long. A remote shutter can be a big help because once you switch to your camera’s bulb mode and click the remote, it will keep the shutter open for more than the camera’s 30 second limitation. Otherwise you’ll have to hold the shutter down with your finger or some sort of tape/pebble mechanism … just use a remote. They’re cheap.
As mentioned before, your aperture should be as wide as it will go.
Because the camera’s shutter will be open for so long and the lens’ aperture is wide open, the ISO can remain relatively low. ISO’s of 100 to 500 are completely acceptable. I wouldn’t go much higher though; there’ll be too much light otherwise.
With these settings you’ll have a very clean photograph of the night sky and some beautiful star trails. Another tip: Find Polaris. The North Star. Your star trails will look especially cool with that in the photo. Go out and try it and you’ll see why.
To take a photograph of the night sky without the stars moving (too much) in your photograph, you’ll want to set up your rig similarly to how you would if you were shooting star trails. The only difference is that your ISO is going to be cranked and your shutter speed is going to be a lot shorter in duration. An ISO of 2,000 to 6,400 is acceptable.
Your shutter speed is dependent on the focal length of your lens too. If you’re shooting a photo with a focal length of 16mm, your shutter speed can be a touch longer because motion will be less evident with a wide angle. If you’re shooting a photo with a focal length of 300mm, your shutter speed will need to be shorter to avoid too much motion from the stars in the frame.
A good rule to follow is the 500 rule. If you divide the focal length of your lens by 500 you’ll get the amount of time your shutter should stay open before star trails start to occur.
At 16mm you can keep your shutter open for roughly 30 seconds. At 300mm you can keep your shutter open for roughly two seconds.
That’s a huge difference.
The best way to learn how to shoot long exposure photography is to go out and do it. I spent a lot of time during my college years outside messing around with long exposures. Much of that time was spent in front of my best friend’s house with a flashlight creating light trails by dancing around like a moron.
Actually, that’s a great idea: Next month’s post is going to continue on with long exposure photography. This time we’ll point our cameras back to earth to capture light trails. See you then!
Justin McKee is a small-town photographer with big ideas living in Michigan. In addition to portraits, wedding photography and video, he also enjoys wildlife photography. He always seeks to learn more about his craft.