Photography Basics: Exposure
by Robert Meeks
I had originally written an article on exposure intended to provide a foundation of the basics for novice photographers. Someone had pointed out that it was perhaps a bit too complex for absolute beginners not familiar with some of the terms used in photography; hence, I wrote this simpler introduction to exposure in photography.
One of the most common terms someone will encounter when getting into photography is the term 'stop'. Aside from jokes about paparazzi being told this several times, a stop is actually referring to exposure.
A stop originally was a reference to the aperture in a lens. In the early days of lens development, even before photography, a lens was often a single or double element (piece of glass) which did not provide a very sharp image due to the center of the lens providing a sharper image than the surrounding portion of the lens. Since the lower sharpness of the outer portion of the lens would reduce the sharpness of the image produced by the lens, someone came up with the idea of blocking or 'stopping' the light which would pass through the outer portion of the lens by placing a metal disk with a hole in it between the lens elements. This metal disk was called a 'stop'. Since a 'stop' also reduces the amount of light which passes through the lens in a given amount of time, it also requires more time to expose film as the size of the stop decreases.
We now use the term 'stop' as a reference for exposure differences.
Exposure differences can be caused by adjusting the amount of time the film is exposed (shutter speed) or by varying the size of the opening in the lens (aperture).
Cameras and lenses use shutter speeds and apertures which have a difference of 2. Either twice as much or half as much. This is also the same value ascribed to a stop.
For shutter speed, we are adjusting the amount of time which the film is exposed to light. If we, for example, are using a shutter speed of 1 second, then we decide to use a shutter speed of 2 seconds, we have increased the exposure by 1 stop; meaning that we doubled the amount of time we were exposing the film. If we were using a shutter speed of 1 second, then we decided to use a shutter speed of 1/2 second, we have decreased the exposure by 1 stop; meaning that we cut the amount of time we were exposing the film in half.
Shutter speeds on a camera which can be selected manually have a difference of one stop between them. You can see this in the amount of time of each shutter speed: 1 second, 1/2 second 1/4 second, 1/8 second, and so on.
Aperture is a little more difficult as the numbers are a relation of the opening in the aperture blades to the focal length of the lens, but the aperture number on each lens means the same thing, regardless of the focal length of the lens; so we can completely forget about focal length when it comes to exposure.
Since the aperture marks on a lens are a difference of one stop of exposure, a larger number meaning less light reaches the film, we can adjust the aperture to control the amount of light which reaches the film. If we are shooting with the lens set at 5.6, then we decide to shoot with the lens set a 8, we are allowing one stop less light to reach the film; meaning half as much. If we are shooting with the lens set at 5.6, then we decide to shoot with the lens set at 4, we are allowing one stop more light to reach the film; meaning twice as much light.
*The numbers representing the aperture on a lens barrel are actually fractions. Hence, a larger number on the barrel is actually a smaller opening in the aperture. An f/8 is smaller than an f/5.6; if the numbers confuse you, just put a '1' in front of the number and it will be easier to remember that 1/5.6 is larger than 1/8. The standard scale of aperture on lenses can range, from largest opening to smallest, as follows: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32. Each difference in one number position (e.g. from a 4 to a 5.6) is one stop.
We can see that adjusting the shutter speed and aperture can both control the amount of light which reaches the film. We can use these in combination to control the amount of light which reaches the film. By decreasing the aperture from 5.6 to 8, and the shutter speed from 1/125 to 1/60, we have decreased the exposure by a total of two stops; as we dropped the aperture and the shutter speed each by one stop.
Do keep in mind that stops is a measure of how we can manually adjust the exposure we are providing for the film and not a measure of the amount of exposure which is required by the film for a particular lighting condition. We get the amount of exposure required from the built in meter on our camera or an eternal meter which tells us where we can set our shutter speed and aperture.
Knowing that each adjustment in aperture or shutter speed decreases or increases the exposure by the same amount, we can use this to adjust the exposure if necessary. If we have set our camera, according to our meter reading, for an exposure of 1/60 second at f/11 (1/60 second shutter speed, f/11 or 11 aperture) and we decide that we need a faster shutter speed to capture an action shot, we can increase the shutter speed by one stop for each stop we adjust the aperture. Being that we know that each increase in shutter speed reduces the exposure by 1/2 (1 stop) (example: 1/125 second gives us half as much time as 1/60 second), then to compensate, we need the increase the amount of light which passes through the lens by by twice as much (1 stop) (example: an f/4 aperture allows twice as much light through the lens as an f/5.6). For our example above, where we have our camera set at 1/60 second at f/11, we can get the same exposure value by setting the camera at 1/125 second at f/8, 1/250 second at f/5.6, 1/500 second at f/4, 1/1000 second at f/2.8, and 1/2000 second at f/2.
Film speed also has an equivalent difference of one stop between film speeds when there is a difference of 2 in the film speed. a 200 speed film is twice as fast as a 100 speed film; meaning that a 200 speed film would allow us one stop more exposure with which to play. Conversely, a 400 speed film is 4 times faster than a 100 speed film which gives us 2 stops more exposure with which to play. This becomes important when we may need extra exposure capabilities due to the lighting conditions. Say that we are shooting indoors with lighting conditions which would give us an exposure of 1/15 second at f/2 (providing that is the maximum aperture at which we can set the lens) using a 100 speed film, we would be challenged to get a sharp image if we had to handhold the camera. If we used a 400 speed film instead, this would give us 2 stops more exposure allowing us to use a faster shutter speed of 1/60 second (1/15 to 1/30 is one stop, and 1/30 to 1/60 is one more stop. Hence, we have decreased the shutter speed by 2 stops, which is the same amount of increase the film has given us.
I hope this has provided some understanding for you with regard to exposure in photography. It is the basic knowledge upon which we can build. Having an understanding of exposure provides us with a base upon which we can add. You should be able to take these basic steps and adjust them according to the needs of the moment to get a proper exposure. Beyond that, you can even develop your own techniques by playing with the exposure.
Have fun with your photography; and remember that your primary goal is not only for your enjoyment of photography, but also to make certain that everyone involved with your photography can share in your enjoyment.
Bob
This article is copyrighted 2006 by Robert Meeks. All rights reserved. Webmasters are allowed to use this article on their site so long as the content and copyright information stays intact and a link is provided, on the same page as the article, to Zhorkow's CargoShip.
by Robert Meeks
I had originally written an article on exposure intended to provide a foundation of the basics for novice photographers. Someone had pointed out that it was perhaps a bit too complex for absolute beginners not familiar with some of the terms used in photography; hence, I wrote this simpler introduction to exposure in photography.
One of the most common terms someone will encounter when getting into photography is the term 'stop'. Aside from jokes about paparazzi being told this several times, a stop is actually referring to exposure.
A stop originally was a reference to the aperture in a lens. In the early days of lens development, even before photography, a lens was often a single or double element (piece of glass) which did not provide a very sharp image due to the center of the lens providing a sharper image than the surrounding portion of the lens. Since the lower sharpness of the outer portion of the lens would reduce the sharpness of the image produced by the lens, someone came up with the idea of blocking or 'stopping' the light which would pass through the outer portion of the lens by placing a metal disk with a hole in it between the lens elements. This metal disk was called a 'stop'. Since a 'stop' also reduces the amount of light which passes through the lens in a given amount of time, it also requires more time to expose film as the size of the stop decreases.
We now use the term 'stop' as a reference for exposure differences.
Exposure differences can be caused by adjusting the amount of time the film is exposed (shutter speed) or by varying the size of the opening in the lens (aperture).
Cameras and lenses use shutter speeds and apertures which have a difference of 2. Either twice as much or half as much. This is also the same value ascribed to a stop.
For shutter speed, we are adjusting the amount of time which the film is exposed to light. If we, for example, are using a shutter speed of 1 second, then we decide to use a shutter speed of 2 seconds, we have increased the exposure by 1 stop; meaning that we doubled the amount of time we were exposing the film. If we were using a shutter speed of 1 second, then we decided to use a shutter speed of 1/2 second, we have decreased the exposure by 1 stop; meaning that we cut the amount of time we were exposing the film in half.
Shutter speeds on a camera which can be selected manually have a difference of one stop between them. You can see this in the amount of time of each shutter speed: 1 second, 1/2 second 1/4 second, 1/8 second, and so on.
Aperture is a little more difficult as the numbers are a relation of the opening in the aperture blades to the focal length of the lens, but the aperture number on each lens means the same thing, regardless of the focal length of the lens; so we can completely forget about focal length when it comes to exposure.
Since the aperture marks on a lens are a difference of one stop of exposure, a larger number meaning less light reaches the film, we can adjust the aperture to control the amount of light which reaches the film. If we are shooting with the lens set at 5.6, then we decide to shoot with the lens set a 8, we are allowing one stop less light to reach the film; meaning half as much. If we are shooting with the lens set at 5.6, then we decide to shoot with the lens set at 4, we are allowing one stop more light to reach the film; meaning twice as much light.
*The numbers representing the aperture on a lens barrel are actually fractions. Hence, a larger number on the barrel is actually a smaller opening in the aperture. An f/8 is smaller than an f/5.6; if the numbers confuse you, just put a '1' in front of the number and it will be easier to remember that 1/5.6 is larger than 1/8. The standard scale of aperture on lenses can range, from largest opening to smallest, as follows: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32. Each difference in one number position (e.g. from a 4 to a 5.6) is one stop.
We can see that adjusting the shutter speed and aperture can both control the amount of light which reaches the film. We can use these in combination to control the amount of light which reaches the film. By decreasing the aperture from 5.6 to 8, and the shutter speed from 1/125 to 1/60, we have decreased the exposure by a total of two stops; as we dropped the aperture and the shutter speed each by one stop.
Do keep in mind that stops is a measure of how we can manually adjust the exposure we are providing for the film and not a measure of the amount of exposure which is required by the film for a particular lighting condition. We get the amount of exposure required from the built in meter on our camera or an eternal meter which tells us where we can set our shutter speed and aperture.
Knowing that each adjustment in aperture or shutter speed decreases or increases the exposure by the same amount, we can use this to adjust the exposure if necessary. If we have set our camera, according to our meter reading, for an exposure of 1/60 second at f/11 (1/60 second shutter speed, f/11 or 11 aperture) and we decide that we need a faster shutter speed to capture an action shot, we can increase the shutter speed by one stop for each stop we adjust the aperture. Being that we know that each increase in shutter speed reduces the exposure by 1/2 (1 stop) (example: 1/125 second gives us half as much time as 1/60 second), then to compensate, we need the increase the amount of light which passes through the lens by by twice as much (1 stop) (example: an f/4 aperture allows twice as much light through the lens as an f/5.6). For our example above, where we have our camera set at 1/60 second at f/11, we can get the same exposure value by setting the camera at 1/125 second at f/8, 1/250 second at f/5.6, 1/500 second at f/4, 1/1000 second at f/2.8, and 1/2000 second at f/2.
Film speed also has an equivalent difference of one stop between film speeds when there is a difference of 2 in the film speed. a 200 speed film is twice as fast as a 100 speed film; meaning that a 200 speed film would allow us one stop more exposure with which to play. Conversely, a 400 speed film is 4 times faster than a 100 speed film which gives us 2 stops more exposure with which to play. This becomes important when we may need extra exposure capabilities due to the lighting conditions. Say that we are shooting indoors with lighting conditions which would give us an exposure of 1/15 second at f/2 (providing that is the maximum aperture at which we can set the lens) using a 100 speed film, we would be challenged to get a sharp image if we had to handhold the camera. If we used a 400 speed film instead, this would give us 2 stops more exposure allowing us to use a faster shutter speed of 1/60 second (1/15 to 1/30 is one stop, and 1/30 to 1/60 is one more stop. Hence, we have decreased the shutter speed by 2 stops, which is the same amount of increase the film has given us.
I hope this has provided some understanding for you with regard to exposure in photography. It is the basic knowledge upon which we can build. Having an understanding of exposure provides us with a base upon which we can add. You should be able to take these basic steps and adjust them according to the needs of the moment to get a proper exposure. Beyond that, you can even develop your own techniques by playing with the exposure.
Have fun with your photography; and remember that your primary goal is not only for your enjoyment of photography, but also to make certain that everyone involved with your photography can share in your enjoyment.
Bob
This article is copyrighted 2006 by Robert Meeks. All rights reserved. Webmasters are allowed to use this article on their site so long as the content and copyright information stays intact and a link is provided, on the same page as the article, to Zhorkow's CargoShip.
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