Long Exposures Can be Worth the Wait
Everyone loves the beauty of long-exposure images like those showing silky, flowing waterfalls. But creating them can seem challenging and perhaps even daunting. Those seconds or minutes the shutter remains open can be nerve-wracking, but when you see the results, the wait can be worth it.
The first thing to consider is your subject. What do you want to photograph, and how should it look? Not just anything will make a successful long-exposure image. Look for scenes that contain an element of motion but also one of stability. It's the contrast between the two that tends to work best. If the entire frame ends up blurred from subject movement, viewers won't have anything relatable to understand what they are seeing. Try to pre-visualize your results, striving for a dynamic tension between movement and stillness. There's a style of impressionistic photography that blurs the entire image by intentionally panning with the shutter open, but that's different from what I'm talking about here.
You're going to need a solid tripod. If you want to preserve an area of stability, you need to hold your camera still. Any camera movement risks ruining your image. Work out your composition, then lock your camera down so it stays put. For best results, use a cable release to fire the camera. Yet curiously, for extremely long exposures, you can sometimes get away without a shutter release cable. Any motion induced by pressing the shutter release button on the camera will dissipate in a fraction of a second and contribute a negligible portion of the overall exposure if the shutter remains open for minutes.
It's also worth considering your shooting location. Sol Duc Falls in Olympic National Park is an iconic location, but you can get the best views from standing on a footbridge over the river below. Because of the site's popularity, I've had several images ruined when a family, not even visible down the trail when I pressed the shutter, set foot on the bridge in the middle of my shot. Tramp, tramp, tramp, the bridge sways up and down. Kids seem to delight in the fun of it, blissfully unaware that a photographer is creating a masterpiece. Anyway, I try, and with enough attempts, I usually get what I'm after.
Use manual focus. Even if you use autofocus to set the focus distance, switch to manual before you shoot. You don't want to find out you flubbed the focus after waiting so long for your masterpiece to materialize. Time spent upfront to get things right is well worth the investment. While you can try again, each attempt can be time consuming.
There is more than one way to achieve long exposure times. As a general rule, use ISO as your first variable. Lower ISO values yield sharper images anyway, so start there before using other means to slow down the shutter speed. Aperture directly affects exposure, too, but resist the temptation to ratchet it down right away. Small f-stop openings can also lessen sharpness through diffraction.
Especially during the day, you'll benefit from using a solid, neutral-density filter. By cutting the light allowed to enter the lens, you'll automatically need longer exposure times. If you can afford it, a variable ND filter can make your job easier. A good one will be costly but will let you dial in the exposure time you want independent of all other variables.
If possible, shoot on a calm day. Even the slightest gust of wind will rustle surrounding vegetation and risk ruining an image. Ultimately, you have little choice but to work with what nature deals you, but a breeze does set a limit on how long you can safely leave the shutter open.
Do, how long should your exposure be? Experience will be your best guide, but sometimes it can simply be fun to experiment and see what happens.
If you find exposure challenging to determine, try taking test shots at more traditional shutter speeds first. Once you're happy they aren't over or under-exposed, work backward from there. Exposure variables have a reciprocal relationship to each other. For example, if you need to quadruple the exposure time, you'll need to stop the aperture down by four stops to compensate. This relationship is known as the "exposure triangle." Film capture was notorious for a phenomenon known as "reciprocity failure," where this relationship broke down, and you had to add more time than your math showed. Thankfully, digital photography is nearly immune to this problem. With digital, you can safely double and halve your way from one combination of exposure variables to another.
Settings on most cameras top out at 30 seconds of exposure time. Beyond that, you'll need to resort to "bulb" mode. The term originated in the early days of photography when cameras used a pneumatic shutter release with a rubber bulb at the end of a tube. Squeezing and releasing the bulb, fired the shutter. Long exposures typically involved locking the bulb with a clamp until the required time ended. Electronic cable releases often have an equivalent locking lever to hold the shutter open. The latest answer comes from a digital timer that serves as a countdown clock. Many newer camera models also support a connection to a laptop computer to control shutter speed. The choice is yours.
Some cameras can leak light through their optical viewfinder, while others seem immune to the problem. If you find your images ghosted and lower in contrast than you expect or suffering from overexposure along one side, try covering the viewfinder during the shot. Your camera may have come with a small, plastic viewfinder cover for just this purpose, but almost anything will do. I often just throw a black hand towel over mine to shield any stray light. If you're shooting mirrorless, you needn't worry since your camera doesn't even have an optical viewfinder.
Shoot your images in RAW mode rather than jpeg. Longer exposures can sometimes suffer from noise. The tools and horsepower on your computer to remove noise far exceed the best effort your camera can muster. And shooting RAW provides you more latitude to correct any exposure problems during conversion. With jpeg, your camera bakes the exposure in before an image makes its way to your memory card. While you can adjust brightness post-capture for jpeg images, the results will almost certainly be inferior.
Long-exposure images provide a great way to show us the world in a way we rarely see it. Sometimes, they can be challenging to capture, but the results can be worth the wait.