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May 28, 2008 - Dave Hecei
As we discussed before, to get proper exposure, the camera's meter reads the Exposure Value (EV) of a scene and selects the proper combination of aperture and shutter speed. We've talked about the first half, aperture, now lets discuss the other half. The other half is, of course, shutter speed.
The camera's shutter controls the amount of light hitting the sensor, or film, by regulating the amount of time that light passes through. This time value is the shutter speed. Faster shutter speeds will let in less light, while slower speeds more light. On modern DSLRs, the shutter speed can be anywhere from several seconds to as fast as 1/8000th of a second. On some cameras, there is also a Bulb (or just B) setting that allows you to have the shutter open for as long as the shutter button is depressed.
The aperture of a lens has standard f-stops so it makes sense that there are standard shutter speeds. A typical speed range is: 30s, 15s, 8s, 4s, 2s, 1s, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, 1/4000, and 1/8000 (the s is for full seconds). Also, just like the f-stops, one step up or down in shutter speeds is considered on stop of exposure. Going from 1/125 to 1/250 is one stop less light. Going from 1/125 to 1/60 is one stop more light.
The shutter speed you choose does have another effect on the photos you take. When the shutter fires, and makes an exposure, a moment in time is saved. You need to use a higher shutter speed if there is plenty of action in the photo, something over 1/250 (this number changes depending of the focal length of the lens you are using). This allows you to freeze the action and get a sharp image. If you want to emphasize this motion, then you will want to use a slower shutter speed.
There is a important rule, or guideline, in photography that you should know about shutter speeds. Even the most steady person cannot hold a camera perfectly still. There will always some movement and that can make for a blurry photo. The rule states that you should use a shutter speed that is equal to or faster than 1 over the focal length of the lens. So if you have a zoom lens that is set at 200mm, you will want to use a shutter speed of 1/200 or faster. The nice thing about modern DSLRs, they take into account the focal length of the lens and usually choose a high enough shutter speed.
There might be a time when you try to take a photo and there is not enough light to allow for a fast enough shutter speed. As long as the subject is not moving you can mount your camera on a tripod. A tripod is used to hold the camera perfectly still while you make an exposure. To get the best results with a tripod, you should use a cable release or remote trigger. This allows you to fire the shutter without touching the camera, which can jiggle it and cause blurry photos.
One of my favorite things to shoot using a tripod is water. By mounting my camera on a tripod and shooting a waterfall, or small stream, with a slow shutter speed (1/4 to 1sec) the water becomes cloud like. This also works with clouds, waves, or even steam.
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