Shutter speed refers to the length of time a camera shutter remains open. The shutter is located in front of a digital camera's sensor and prevents light from reaching that sensor until the shutter release button (or self timer) opens it. The amount of time the shutter remains open is variable and expressed in fractions of a second known as shutter speed. A typical average shutter speed is 1/125 of a second. We usually refer to slow shutter speeds as those that are 1/30 of a second and slower. It used to be an adage that one could not hold a camera steady enough to get a sharp photograph when using a shutter speed slower than 1/60 second. However, technology such as image stabilization make today's cameras capable of obtaining sharp photographs with slower shutter speeds, that is—up to a point. Most all point and shoot caneras will allow the shutter to remain open longer than anyone can hand hold a camera and obtain a perfectly sharp shot. It is with these slow speeds that I urged you to experiment with last post.
By the way, why does the shutter stay open longer in lower light? The reason is that the amount of time the shutter remains open is one way the camera controls the amount of light reaching the sensor. Bright light makes a proper exposure quickly. Dim light makes a proper exposure slowly.
What is the another way a camera controls the exposure? The size of the opening in the lens is called the aperture. The camera aperture works just like the pupil in you eye. I'll talk more about aperture in a later post.
One last thought. The other variable in exposure control is ISO, formerly and sometimes still referred to as film speed. More on that later.
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