|Trees at Sunrise
- You can use a slow shutter speed to create a pleasing motion blur--such as the silky effect on a waterfall.
- You can use a fast shutter speed to freeze motion, like a kayaker on rapids.
- You can use a large aperture (small f/stop) to create photographs with a shallow depth of field, like a butterfly with a blurry background.
- You can use a small aperture (large f/stop) to to create photographs with both the foreground and background in focus, like a cascade with waterfall in the background.
Let's consider the above photograph. For this photograph, I wanted a relatively fast shutters speed because I was handholding my camera and there was very little light. However, I also wanted to shoot at a low ISO to keep noise down on my point and shoot camera (I shot this with a Canon S100HS). I didn't need a large f/stop, so I could let in light with a larger aperture (smaller f/stop) to keep my ISO low and my shutter speed reasonable. So I set my ISO to 200 and my f/stop to f/3.2. The camera's light meter then calculated a proper exposure with a shutter speed of 1/60sec.
Here was my proper exposure:
SS 1/60sec F/stop f/3.2 ISO 200
If I wanted a faster shutter speed, I could have raised my ISO to 800 (a change in two stops). This would allow me to make my shutter speed a faster 1/250sec. So If I wanted to shoot this scene with a shutter speed of 1/250sec and an f/stop of f/3.2, I could raise my ISO to 800 and maintain the same properly balanced exposure. The exposure is the same--the same amount of light is hitting the sensor--but there would be an affect on the image. The most noticable difference would be an increase of noise from my point and shoot camera.