Long exposure photography is something most hobbyists have tried at some point or another. Slow shutter speeds are necessary, after all, for capturing flash-free images after dark. But long exposures aren't just for low light. Those surreal-looking photos of streaky skies and misty waters are long exposures, too. Let's see how to take them!
[ Top image Things will never be the same by Flickr user Garry - www.visionandimagination.com]
Long exposure photography can be divided into two categories: photos taken during the day, and those taken at night. While many of the techniques used for both types of photography are the same, there are also some significant differences.
Tips for both types:
Use a sturdy tripod. This should really go without saying, but the tripod you use could make a big difference to your final photograph. A lightweight or cheap tripod may add camera shake to your image, especially if there's a breeze or you're using your hands to release the shutter. Make sure that your tripod is solidly placed on the ground--it doesn't have to be completely level ground, but the tripod should be positioned securely enough that it doesn't wobble when touched. If you're shooting in particularly windy conditions, you may need to put some kind of weight on top of your camera to prevent not just camera shake but the possibility that the wind will knock your whole kit to the ground.
Use a remote or cable release. With particularly long exposures this doesn't matter quite so much, since the amount of time that your hand is touching the camera is going to be minor compared to the amount of time that that shutter is actually open, and probably won't affect the exposure. For shorter exposures, however, it will matter - so make sure you bring one along.
Shoot in RAW. During daytime exposures, ND filters can create unwanted color casts in your images, which can be more easily corrected in post processing. During nighttime exposures, your white balance sensor may not function correctly, so that RAW format will give you more flexibility to correct for that later on. You'll also get more dynamic range in a RAW image, which is useful for either type of exposure.
Bright Atlanta by Flickr user Nrbelex
Don't forget about composition. It can be easy to get caught up in imagining what all that motion is going to look like in your final image, but make sure you remember to compose with those stationary objects in mind as well. Use good composition--provide your viewer with some perspective by placing something in the foreground, for example, or include leading lines. Think about what your image would look like if it wasn't a long exposure, and then go from there.
Have a clean sensor. Since you'll probably be shooting at smaller apertures, any dust and other spots on your sensor are going to be very obvious in your photograph. Unless you are particularly fond of that little cloning tool in Photoshop, you want to avoid having to remove those spots after the fact. If your camera has a sensor-cleaning function, make sure you use it just before you go out (you should be using it regularly anyway). If your sensor gets too dirty don't try to clean it yourself. Take it back to the manufacturer to be cleaned, or to your local camera shop if you have one nearby that's certified by your manufacturer.
Tips for daytime long exposures
Use a neutral density (ND) filter. ND filters come in different stops, so the one you choose will depend on how bright the day is and how long you want the exposure to be.
Long exposure shot of a small cascade on the Virgin River, Zion National Park by Flickr user Alaskan Dude
Focus first. If you're using a particularly dense ND filter you may not be able to autofocus, and you may even have a difficult time manually focusing. This is because only a small amount of light can pass through a ND filter, and your autofocus system needs more light to be able to function. Your eye does, too. So in most cases you will need to remove your ND filter, compose and focus the shot manually, then replace the filter and shoot. Don't use autofocus for this step, since your camera will try to refocus the shot after you replace the filter, thus screwing up everything you just did.
Use NDCalc. This app is available for iPhone and for Android, and is a very simple tool to help you get the correct exposure with your ND filter attached. To use NDCalc, take a reading with your camera's meter (without the ND filter). Then tell NDCalc what exposure time your camera came up with, and which ND filter you're using. The app will then tell you how long the exposure should be.
You can do this manually, too, of course - you'll need an ND filter exposure chart (like this one) or a brain that's particularly good at math.
The magic hour counts here, too. Even with daytime long exposures it's still better to take your photos during the hour just after sunrise or just before sunset. You will get much better contrast in the clouds, which will make any movement there more dramatic.
Think about your goals. If your goal is to capture that soft, misty look in the water, the weather isn't going to matter so much. But if you want to capture movement in the clouds you will need to choose a partly cloudy day with a decent wind. A fully overcast day won't give you that beautiful streaky look because there is too much cloud, while a day without any wind will give you only very limited movement in the sky.
Tips for nighttime long exposures
Pay attention to ambient light. Except in the case of very dark, moonless nights, there is almost always going to be some ambient light in your scene. Your eye is not going to interpret that light in the same way as your camera does, so it's helpful to become familiar with how the different types of light are going to affect your scene. A full moon, for example, will bathe your whole scene in a soft light. Light pollution from a nearby city, on the other hand, may add an unpleasant cast to your horizon or make it difficult for you to capture stars.
Know your ISO. With daytime long exposure photography, you generally want to keep your ISO as low as possible. This is also true for nighttime long exposures, but give yourself a little more flexibility. You will get some additional noise at the higher ISOs, and long exposures can also create noise. But depending on how much ambient light is in your scene you may not be able to use those small ISOs you use during the day. Experiment with different ISOs until you get an exposure you're happy with, and generally try to keep that ISO as low as you can.
Focus to infinity. As when shooting with an ND filter, it can be tough to get focus and composition right when you're shooting in dark conditions. Since you're shooting digital, you can throw away a few frames to make sure you get this right. Focus, compose, and turn up your ISO as high as it will go. Take whatever exposure your camera tells you to and then check it on your LCD screen for focus and composition. Make adjustments if necessary, then turn down your ISO and do some real shooting.
Motion is often the name of the game with long exposures of any kind. At night you may want to capture star trails, or the lights of passing vehicles. During the day you may want to capture the motion of crowds of people, or the passing clouds and moving water. The trick is to be able to visualize how this motion will look at a long exposure, and incorporate that into your composition. This is a different way of visualizing photography than your standard during-the-day stuff, so practice and experimentation is going to be very useful. Eventually you'll learn to see a long exposure the way your camera does - and that's when you'll start taking excellent photos.
Also see my selection of 25 outstanding long exposure photographs.
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