The secondary effect with the easiest of the three to understand is probably the shutter speed.
- A fast shutter speed can freeze action.
- A slow shutter speed will blur motion.
If you are shooting sports, chances are you are going to want to freeze their motion. To freeze motions that a person can do, your shutter speed needs to be at least 1/640 second. This will freeze a scene with small human motions in it, for example, a jogger or a friendly game of Ping-Pong. Faster shutter speeds will freeze quicker motion, for example, the moving arm of a baseball pitcher or a sprinter.
If you are shooting a waterfall, chances are you are going to want to let the motion of the water blur out a little bit. ½ second is a little bit of blur; an exposure of several seconds will turn moving water into a misty, creamy blob.
There is a down side to this secondary effect: Camera motion. Generally, one wants the camera to be perfectly still during an exposure. For example, the camera in this waterfall picture had to have been secured to a good, solid tripod during the exposure. Here is an image grabbed from the Internet that shows what camera motion blur looks like.
There are several technical ways to avoid camera shake.
- Use a high shutter speed. The rule of thumb is to use a shutter speed whose denominator is greater than the focal length in millimeters. That is, for a 100mm lens, shoot at 1/100 second or faster.
- Use a tripod.
- Use “image stabilization” (as it is called in the Canon world; also known as “vibration reduction” (Nikon) and “optical steady shot” (Sony)).
Next: Secondary effect: ISO