Friday, October 9, 2009

Exposure 101: Part 3
The Aperture and Shutter Speed

The art of photography comes in the balance of light and time. The magical box that allows us to record history, a moment in time, with the mere push of a button is an amazing achievement. The camera in your hands can create images that also convey an emotion, perspective, inspiration, fascination, the list goes on. Gone are the days of worrying about running out of film. You have 24 rolls of film now, and it's reusable. Push the button. You have a rechargeable battery. Push the button.

So, a camera has an aperture in the lens that lets in different amounts light and controls if the background is blurred or clear. The camera also has a shutter that blocks the light until the button is pushed. The shutter controls how long the light passing through the lens will be allowed onto a sensor: the faster the movement, the faster the shutter speed needs to be to freeze the action. The combination of how much light, (aperture,) and amount of time, (shutter speed,) create an exposure.

A "correct" exposure means that the balance between aperture and shutter speed leaves your subject not too bright, nor too dark. If your subject is too bright, or overexposed, then too much light was coming through the aperture or the shutter speed was too long. Conversely, if your subject is too dark, or underexposed, then the aperture didn't let enough light through or the shutter speed was too fast.

For most photography exposures, as more light is allowed through the aperture, a faster shutter speed will be needed to balance the exposure. If less light is allowed through the aperture, (a higher f/stop number,) then a slower shutter speed will be needed for balance. If a faster shutter speed is desired, then the camera will need to open up the aperture, (lower f/stop number.) If a slower shutter speed is used, then the camera will need to close down the aperture, (higher f/stop number,) for balance. Simply stated, as one number goes up, the other must come down.

Keep in mind that when you are looking at the shutter speed on your camera, it might read, for example, 1/60 or just 60, but they both mean 1/60th of a second. As we start exploring the different functions and settings on your camera, what you choose to tell the camera what you're taking a picture of is going to affect either the shutter speed or the aperture. There are no extra components that a "professional photographer" has on their camera that you don't have, except for more shutter speeds and f/stops available to choose from. Shutter speed and f/stop, that's it. But there is another aspect in photography that can affect the f/stop and shutter speed, the film speed or "ISO."

In our next installment, we will see how the ability to change the camera's sensitivity to light, or ISO, with every picture has dramatically changed the world of photography with digital cameras. We will also start digging in to the automatic settings on your camera to see how they will affect the f/stop and shutter speeds for different types of pictures.



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