|
|
 |
 |
|
Exposure |
| Exposure Modes are incorporated mostly into SLRs, but some compact cameras also use them. These modes tell the camera, whether it can automatically adjust exposure or if you are going adjust exposure manually. There are also different levels of manual. With most cameras, you can set one part of the exposure and have the camera calculate the other. With all of this, you are using the camera's light meter to measure the amount of light in the scene. |
Auto: Exactly how is sounds. The camera does everything. In this mode many cameras will even automatically use the flash. Most cameras have this mode, sometimes it may not be labeled as "Auto." Check your camera's manual for more information.
Program [P]: The camera chooses both the shutter speed and aperture. Typically, given that there is enough light, the camera will choose a exposure which can be handheld. The difference between this mode and Auto is, most camera lock you into Auto. This means that you cannot change anything in Auto. Program usually allows some changes to be made such as using the flash.
Aperture Priority [Av] or [A]: The photographer chooses the aperture and the camera chooses the shutter speed. Since the aperture can have an effect on focus as well, many advanced users will use this setting.
Shutter Priority [TV] or [S]: The photographer chooses the shutter speed and the camera chooses the aperture. This is a good mode for sports or wildlife because a fast shutter speed is needed to freeze action.
Manual [M]: The photographer selects both aperture and shutter speed. This gives the photographer the most control. The camera's internal light meter will tell you if the picture is well exposed or not for the metered area. This mode also allows the camera to be overridden to acheive a specific effect.
|
|
|
|
|
|
|
|
|
Exposure is how the image gets recorded. Cameras have the ability to calculate the exposure automatically. There are four main factors that drive exposure. Shutter Speed, Aperture, ISO/ Sensitivity and the amount of light in a scene. Definition: A Stop is an increment of change in exposure. Apertures, Shutter Speeds, and ISO/ Sensivity are measured in stops. Each time a stop is changed, the amount of light entering the camera is either halved or doubled. Stops are the building blocks for exposure, you will see this term again and again.
Stops are interchangable. If you increase the shutter speed, that is the same as decreasing the ISO or increasing the aperture. A stop changed on any of the main factors for exposure essentially accomplishes the same thing, halving or doubling the light entering the camera. If you were to increase the shutter speed and decrease the aperture, the amount of light entering the camera, is the same as before you changed it. You may ask, why the seperate devices for creating exposure, if they accomplish the same thing? The reason is, shutter speeds control light differently than apertures which are different from the ISO/ sensitivity. The combinations of those different types of control creates the exposure. Try experimenting with changing both the aperture and the shutter speed in equal amounts to see the effect the aperture and shutter speed has on the picture. You may notice that at lower apertures you get more light but less focus. With shutter speed, you may get motion blur at lower shutter speeds and the ability to freeze action at faster speeds. |
|
Shutter Speed and aperture are the 2 main functions controlled by the camera, which can be changed to create exposure. The ISO or Sensitivity usually remains a fixed value. Going back to film cameras, a roll of film had 24 or 36 shots, which had to be used before the ISO could be changed. With digital cameras, the sensisitivity can be changed manually per shot or the camera can adjust per shot in "Auto." Low ISO settings will render the sharpest pictures and the best color saturation. High sensitivity settings are better in low light and for action. However, pictures can suffer from noise, lower contrast, and sometimes desaturated color. It is usually reccommended to shoot on the lowest ISO setting possible for the lighting conditions. Raise the ISO only if you need help to increase the shutter speed for low light conditions or for action. |
The shutter is the mechanism in the camera which opens and closes to allow light to strike the sensor. Check out the Digital Basics Section to learn about sensors. The shutter operates at fractions of a second. When shutter speeds are written as a whole number, that really refers to a fraction. Example: 1/1 = 1 second, 1/2, 1/4, 1/10, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000. These are whole stop shutter speeds. Some cameras may have more increments than the standard whole stops. Most SLRs currently use 1/3 stop increments to get a more accurate exposure. Any shutter speed below 1/30 of a second should be mounted on a tripod to prevent handshake. Slower shutter speeds can have a neat effect by blurring the motion of the subject. Shutter speeds over 1/250 are usually required to freeze action. This would be the case in sports and wildlife photography.
Notice in the pictures on the right, the fast shutter on the top picture froze the truck in motion. The slow shutter on the bottom picture, gave the water a shimmering silky look.
|
|
|
|
|
|
|
|
|
The aperture is the iris built into the lens. The iris opens and closes to increase or decrease the amount of light entering the lens. Apertures, also measured in stops, look like: f/1.4, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32. Once again, more stops may be represented on your camera, becuase cameras have the ability to measure in 1/3 stops. The "f" goes before each number to represent the number as a aperture. Trivia answer: The "f" represents a complex ratio between the diameter of the aperture and the distance to the sensor. But for this explanation you do not need to know that. The aperture also controls depth of field, which is how deep into the picture the focus goes. See the SLR section on focus for more information on depth of field. A low number will have a focus depth of just a few inches, where a larger f/ stop can focus to infinity. Low aperture settings mean the largest hole and the most amount of light. High aperture settings mean the smallest hole and the least amount of light.
(The picture on the bottom has a very shallow depth of field. This makes the background out of focus. This picture was taken using an aperture of f/2.8.) |
|
|
| Make a notebook. To help learning exposure, get a notebook and write down all the exposure settings per image. Digital cameras make this a little easier, because many digital cameras have the exposure information built into the file. A notebook will allow you to see a patterns in your exposure. It will also help you remember what settings you needed to get that neat picture. |
|
|
|
