Understanding The Shutter
The shutter is a device that is in front of the digital sensor. This device works like a curtain when it is closed it will block light from hitting the sensor and when it is open it will allow light to fall onto the sensor. In most cases there are two curtains on rollers that move at a constant speed, determining each exposure's length of time. This length of time is called shutter speed. Shutter speed is measured in seconds – in most cases, fractions of seconds.
This action of opening the shutter allows light to enter the chamber where the digital sensor is located. Many photographers know how to control this speed, which allows them to dramatically change the way the image looks. Each shutter speed has its own attributes which a photographer can use to their advantage. The slower the shutter speed the more movement in an image. The faster the shutter the more likely hood that the image will stop all motion in an image.
While the shutter speed can control the amount of movement in an image it can also control the amount of light that is allowed to fall onto the digital sensor. The faster the shutter speed the less light that is able to hit the sensor. The slower the shutter speed the more light is allowed to fall onto the sensor. This can have a direct effect on the exposure of the image. An image that is brighter than it should be can be considered overexposed. This happens when too much light is allowed during exposure in which the result is an overly bright image. An image that is too dark than it should be can be considered underexposed. This happens when not enough light is allowed during exposure, and the result is a dark image. To avoid this consider using shutter priority while learning how to use the different shutter speeds.
Understanding Shutter Priority
The above diagram shows the shutter speed and its respected effect. Notice that the bigger denominator has a faster speed; likewise, the smaller denominator has a slower speed (i.e., 1/1000 is much faster than 1/200). Keep in mind that when you have a faster speed, you let less light in, but you will be stopping action; the slower the shutter speed, the more light is allowed to pass through, and the more blur you will get in the image.
The photographer also needs to consider what effect they want on the end image. This is done by determining how the photographer wants to capture the subject. A few questions to think about are: Is the subject moving? Is the background moving? Am I moving? Do I want to stop action? Do I want to show action by showing some blur? Does my subject have enough light? These are the questions a photographer needs to consider before setting their shutter speed.
To freeze movement in an image, the photographer will need to choose a fast shutter speed. A speed of 1/500 or higher is considered a fast shutter speed. At 1/250, you begin to stop slower actions (i.e., someone waving their hand). When picking the shutter speed, it is always important to remember that you are blocking out the light; the faster the shutter speed, the more light is blocked. The slower the speed, the more light is let in.
To let motion blur in an image, you will want to choose a slower shutter speed. The actual speeds will depend on the subject. This is because the speed will change depending upon the speed of the subject and how much blur the photographer wants in the image. A slower shutter is 1/100 or slower; keep in mind that anything below 1/60 is not handheld, and you will be getting more light onto the digital sensor. Thus, your image will be getting brighter.
When the photographer is ready to take the camera out of Shutter Priority and place it into manual mode, they must think about how the shutter will affect the end exposure. Exposure is the amount of light that reaches the surface of an image sensor, as established by shutter speed, aperture, and ISO which is determined by the scene luminance
Exposure is measured by multiplying the exposure rate by the Exposure time this is called a stop. Each stop of light is equal to double the amount of light. If you want to add light to a scene you will open one stop by slowing down your shutter which means the camera will be doubling the amount of light allowed through the shutter. In contrast if you want to block light from a scene the camera will be stopping down by choosing a faster shutter. There is no such thing as the "perfect" exposure time, only the right exposure for the photograph you are creating.
The photographer also needs to consider camera movement; every camera will move when taking a photo even if it is on a tripod. This is called camera shake. To counter this movement, the photographer will need to set their shutter speed to a hand-held speed.
A hand-held speed is the slowest shutter speed a person can reasonably hold a camera and not show any movement from pressing the shutter button. To achieve this speed the camera needs to be set at 1/60 of a second or faster. If the shutter is any slower then 1/60 of second it will become difficult to use without getting camera shake. If the camera needs to be on a slow shutter speed (anything slower than 1/60), it is best to use a tripod to steady the camera.