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PhotographyJam - the photographer's resource: Camera basics: shutter-speed, aperture and ISO
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Camera basics: shutter-speed, aperture and ISO · by Simon Mackie

In this article, I’ll introduce you to the basic elements that you can use to control exposure in your shooting. If you have a digital SLR, there will be a way to set all of these controls on your camera, but since they differ between manufacturers and models, you’ll need to refer to your camera’s manual to find out exactly how to change them.

All cameras, whether an ancient film camera, or a more modern digital, work in pretty much the same way. Photographs are taken by letting light fall onto a light-sensitive medium, which records the image. Traditionally, this has been film, but more recently, it tends to be a digital sensor. The more light that falls onto the film or sensor, the lighter the image.

Put simply, a camera consists of a light-tight box that stores a light-sensitive device (either a film or a digital sensor), a lens that magnifies and focuses the image onto that light-sensitive device through a hole in the box (called the aperture) , and a shutter that opens and closes when you press the shutter release, exposing the film or sensor to the light; this is why a picture is sometimes called an exposure.

The amount of light entering the camera depends on the amount of light in the scenes that you’re photographing. A bright sunny cloudless day has more available light than a cloudy one, which in turn has more light than an indoor scene lit by tungsten lighting. To make the picture look right, we have to expose the film or sensor to the right amount of light. Too short, and the image will be dark, or underexposed:

Underexposed, dark image of child and baby

To much light, and it will be overexposed:

Overexposed, too bright image of child and baby

If we get it just right, the image will look similar to what our eyes see:

child and baby

Luckily, our cameras have clever electronics and light meters in them, which take all the guesswork out of this for us and get it right most of the time. If you leave your camera in P, program, or auto mode, you’ll hopefully get correctly exposed pictures all the time. But to get really creative, you need to take control!

With most cameras, except basic “point n shoots” you have three variables that you can control:

  1. Shutter speed
  2. ISO
  3. Aperture

Let’s deal with perhaps the simplest one first, shutter speed.

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