Public Lab Research note


On Long Exposure Photography

by C_Eich | March 02, 2012 00:18 | 156 views | 1 comments | #882 | 156 views | 1 comments | #882 02 Mar 00:18

Read more: publiclab.org/n/882


Long exposure photography has a lot of artistic and scientific potential. Even when its use is scientific, the practice is an art, simple in principle yet depending on a sensitive eye and soft touch. I am writing here a general overview of long exposure photography for still cameras, not for video or webcams using Glow Doodle.

The basics are simple: A camera is a box with a hole in it. To “expose” an image we open up that hole to let light through. In a long exposure photograph the shutter of a camera is kept open for far longer than it is for an ordinary photo (which has a shutter speed of a small fraction of a second). Long exposures can be anywhere from several seconds to many hours. Generally one would want to have the camera on a tripod or at least sitting on something very firm and still. But in the case of the photograph of mine featured here, the exposure was only about 15 seconds and I hand-held the camera. Since long exposure images are often very impressionistic even if a tripod is used, there is a good deal of room for hand holding and having less than perfect stillness. But when holding the camera by hand remember that it is far easier to approach stillness if you are leaning against a wall, tree, or anything firm. I shot this image supporting my elbows with my torso and my back against a wall.

Besides shutter speed, the ISO(speed or light sensitivity of the sensor or film) and the aperture (size of the opening) are the factors determining the exposure. You have to experiment with these, generally using higher ISO and wider aperture when you have less light or a shorter shutter speed. And of course lower ISO and smaller aperture when you have more light or a longer shutter speed. (Keep in mind the smaller aperture notations like f. 2 or f. 2.8 denote the bigger openings. f. 16 is a much smaller hole.) Often when we shoot glowing sorts of things in the dark though, we want max sensitivity, so higher ISOs lke 800 or 1600 are good, and wide apertures. This shortens the necessary shutter time and makes it easier to keep the camera still. The first exposure can be an experiment, especially when shooting digital. Just try, perhaps, 20 seconds and see how it looks. Keep in mind that digital images can be lightened up and improved and more light and details brought out of the shadows especially (as opposed to the highlights) later in digital editing software. With negative film photography it is the opposite—it is better to overexpose, because you can get more information later out of a dense negative with bright highlight areas than out of a thin negative with nothing in the shadows.

In digital photography you have huge room to change your exposure after the fact (lighten or darken the image) and make many other changes later as well if you shoot in RAW and you have RAW editing software. So when shooting long exposure pictures shoot in RAW if your camera can do it. Good digital cameras shooting RAW make it really easy to make good long exposure images.

It’s best to have a camera that allows you to set all settings manually, but it’s not necessary. As long as you can set the shutter speed long you can take long exposure photos. With many cameras you have to physically hold down the shutter button while it exposes (this is Bulb setting, rather than T or Time setting). I have even found a couple long exposure apps for iphones—Magic Shutter and Slow Shutter Cam. I have no iphone but from what I read it seems Slow Shutter Cam might be better suited to these sorts of thermal imaging uses because it’s meant to give more control to the user. I am sure there are other apps out there as well.

Have fun and make some science, or art, or both!


1 Comments

Thanks for this clear and thorough description Chris! I am gonna try it myself.

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