Exposure of a photograph is a matter of how much light registers on the media (film or digital camera sensor) that collects that light. Proper exposure of a photograph depends on the three factors that control how much light is registered: ISO, aperture, and shutter speed. Combining these three variables in the proper proportions will result in the proper exposure of photographs.
ISO is a measure of how sensitive the film or digital sensor is that is collecting the light. The lower the ISO number, the lower the sensitivity. The higher the ISO, the higher the sensitivity.
Aperture refers to the diameter of the diaphragm in the lens of the camera. Similiar in function to the pupil, the wider the diameter (or aperture) is, the more light can enter through the lens to be collected by the sensor. Because aperture is measured as a ratio of focal length of the lens to the diameter of the lens, the aperture setting is expressed as f/(aperture value). A setting of f/2.8 means that the focal length of the lens is 2.8 times the diameter of the diaphragm. The smaller the digits in the expression for aperture, the larger the diaphragm. The larger the number, as in f/8, the smaller the aperture.
Shutter speed is the easiest of the three variables to understand. It is as simple as it sounds. This is the amount of time that the shutter is open to collect light. The longer the shutter is opened, the more light is allowed to pass through the lens to be collected.
All three of these factors come with other benefits or drawbacks depending on how you look at it. These side effects can be put to creative use When fully understood and properly utilized.
Knowledgeable photographers understand the causes and effects of these factors and will set them before ever taking a picture. Usually, a photographer is concerned first with ISO. Higher ISO settings result in grainier images. For this reason most photographers normally keep ISO settings as low as possible. Even though noise and film grain are usually unwanted, sometimes they are used to achieve this effect in the image.
Changing the opening in the diameter of the diaphragm changes how much light passes through the lens and onto the light catching media whether it is film or a digital sensor. When changing the aperture the focus in the image captured is also changed. Smaller apertures such as f/8 and f/16 will result in more area in focus between foreground and background. Called depth of field, this is very important in the capturing of an image. Bigger apertures like f/1.8 and f2.8 narrow the depth of field so that most everything in the final picture will out of focus. This helps to highlight the subject in a dramatic way by leaving the subject in focus while distracting foreground and backgrounds remain out of focus.
Shutter speed regulates how much light passes through the lens by varying how long the shutter is open. Obviously, the longer the shutter is open the more light will pass through the lens on it's way to the film or sensor and vice versa. The side effect of shutter speed is motion blur or lack of. The longer the shutter is open the more the apparent moving parts of the image will blur. Blurring moving subjects or even the entire image using slow shutter speeds can be put to creative use and it often is. Other times a fast shutter speed is required when "freezing" a subject is the desired result.
When these three variables are set properly, a properly exposed image will result. Once set properly, a change in one of the variables will require a change in at least one of the other variables to compensate. This is because changing only one of the variables will increase or decrease the amount of light that lands on the film or sensor or affect the sensitivity of that film or sensor. Increasing the sensitivity, or ISO, of the sensor or film will result in an overexposed photograph if the light landing on that sensor or film is not reduced by increasing the shutter speed or decreasing the aperture. Increasing the shutter speed to freeze a rodeo rider will result in an underexposed photograph unless the size of the aperture is increased to allow more light in or the ISO is increased which results in more sensitivity to the decreased amount of light.
Together, these three factors result in whether or not the picture is properly exposed. A good photographer understands these factors and the effects that they have on the final image. He will use this knowledge and take care to ensure the proper settings are utilized to produce exactly what he wants before he ever presses the shutter release button.
ISO is a measure of how sensitive the film or digital sensor is that is collecting the light. The lower the ISO number, the lower the sensitivity. The higher the ISO, the higher the sensitivity.
Aperture refers to the diameter of the diaphragm in the lens of the camera. Similiar in function to the pupil, the wider the diameter (or aperture) is, the more light can enter through the lens to be collected by the sensor. Because aperture is measured as a ratio of focal length of the lens to the diameter of the lens, the aperture setting is expressed as f/(aperture value). A setting of f/2.8 means that the focal length of the lens is 2.8 times the diameter of the diaphragm. The smaller the digits in the expression for aperture, the larger the diaphragm. The larger the number, as in f/8, the smaller the aperture.
Shutter speed is the easiest of the three variables to understand. It is as simple as it sounds. This is the amount of time that the shutter is open to collect light. The longer the shutter is opened, the more light is allowed to pass through the lens to be collected.
All three of these factors come with other benefits or drawbacks depending on how you look at it. These side effects can be put to creative use When fully understood and properly utilized.
Knowledgeable photographers understand the causes and effects of these factors and will set them before ever taking a picture. Usually, a photographer is concerned first with ISO. Higher ISO settings result in grainier images. For this reason most photographers normally keep ISO settings as low as possible. Even though noise and film grain are usually unwanted, sometimes they are used to achieve this effect in the image.
Changing the opening in the diameter of the diaphragm changes how much light passes through the lens and onto the light catching media whether it is film or a digital sensor. When changing the aperture the focus in the image captured is also changed. Smaller apertures such as f/8 and f/16 will result in more area in focus between foreground and background. Called depth of field, this is very important in the capturing of an image. Bigger apertures like f/1.8 and f2.8 narrow the depth of field so that most everything in the final picture will out of focus. This helps to highlight the subject in a dramatic way by leaving the subject in focus while distracting foreground and backgrounds remain out of focus.
Shutter speed regulates how much light passes through the lens by varying how long the shutter is open. Obviously, the longer the shutter is open the more light will pass through the lens on it's way to the film or sensor and vice versa. The side effect of shutter speed is motion blur or lack of. The longer the shutter is open the more the apparent moving parts of the image will blur. Blurring moving subjects or even the entire image using slow shutter speeds can be put to creative use and it often is. Other times a fast shutter speed is required when "freezing" a subject is the desired result.
When these three variables are set properly, a properly exposed image will result. Once set properly, a change in one of the variables will require a change in at least one of the other variables to compensate. This is because changing only one of the variables will increase or decrease the amount of light that lands on the film or sensor or affect the sensitivity of that film or sensor. Increasing the sensitivity, or ISO, of the sensor or film will result in an overexposed photograph if the light landing on that sensor or film is not reduced by increasing the shutter speed or decreasing the aperture. Increasing the shutter speed to freeze a rodeo rider will result in an underexposed photograph unless the size of the aperture is increased to allow more light in or the ISO is increased which results in more sensitivity to the decreased amount of light.
Together, these three factors result in whether or not the picture is properly exposed. A good photographer understands these factors and the effects that they have on the final image. He will use this knowledge and take care to ensure the proper settings are utilized to produce exactly what he wants before he ever presses the shutter release button.
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