Camera basics: shutter-speed, aperture and ISO · by Simon Mackie
Shutter Speed
The concept of shutterspeed shouldn’t be too hard to grasp. The longer you leave the shutter open for, the more light lands on the film, resulting in a brighter image. On an old-style manual camera, you used to get a shutter speed dial that looked like this:
Those numbers that you see in white are the shutter speeds in fractions of a second, and is the time taken from when the shutter opens to when the shutter closes, after you’ve press the shutter release. The shutter speeds are 1/30th of a second, 1/60th of a second, 1/125th of a second, 1/250th of a second, etc. Moving from one speed to the next one halves the amount of light that can enter the camera. On the other hand, moving the other way, to a slower shutter speed, doubles the amount of light that can get into the camera. The change from one speed to another (and halving or doubling the light that enters the camera) is called moving a stop. So moving from a speed of 1/30th to 1/60th of a second is going 1 stop faster, and from 1/60th of a second to 1/250th of a second is moving 2 stops. Even on more modern SLR cameras, while you may not have a dedicated shutter speed dial, you’ll find that you can select the same shutter speeds as you could on my old film camera above (although you can probably select a wider range of speeds!)
So what affect does changing shutter speed have? As well as controlling the amount of light that enters the camera, shutter speed has another interesting effect – slow shutter speeds show motion and blur, while fast shutter speeds can “freeze” motion.
Here’s an example of taking a picture of a fast moving subject with a slow shutter speed, which as you can see has recorded the motion of the subject quite nicely:
Conversely, if we use a high shutter speed, we can “freeze” the action of this surfer:
So by actively choosing a shutter speed, you can add a creative element to your pictures by showing motion, or you can decide to freeze the image at a decisive moment.
Camera shake
On issue with shutter speed is that choosing a shutter speed that’s too slow can mean that your pictures lose their sharpness due to camera shake. It’s virtually impossible to hold the camera perfectly still while shooting your picture unless you use a tripod. At low shutter speeds, this movement can be seen on your images as a slight blurring which meas that your pictures won’t be as sharp as you’d like. This effect is more noticeable when using zoom or macro lenses, and the longer the zoom, the more pronounced the camera shake will be. So to avoid camera shake, you need to use a high shutter speed.
A good general rule of thumb is that you should use a shutter speed at least as fast as 1/the focal length of your lens. So if you are using a 200mm zoom lens, you should use a shutter speed of at least 1/200th of a second (1/250th of a second on my dial above should be OK)
Shutter speed priority mode
If you’d like to set a given shutter speed and let the camera work out what else is required to get the exposure right, you can use shutter-priority mode. This is normally signified by Tv or S on your mode selection dial (Tv means “time value”). This lets you select a shutter speed and the camera will work out the rest to get a correct exposure.
Ok, so that’s shutter speed. Let’s now move onto looking at aperture.
commenting closed for this article
Exploring the Canon 350D/Rebel XT custom functions The Tilt-Shift Miniature Fake Technique in Photoshop CS: A Simple How-To