Shutter Speed, Aperture, and Depth of Field
By Richard Schneider
Shutter Speed and Aperture are the two most important functions of a camera. If you ever want to be an accomplished photographer it is essential that you learn how these two functions interact with one another. Shutter speed refers to the amount of time the camera sensor or film is exposed to light. Aperture refers to the amount of light that is let into the camera for the sensor or film to collect.
The shutter on a camera is what opens the front of the camera body to expose the image sensor or film to the light flowing through the lens. Shutter speed is the amount of time the shutter stays open to expose the sensor to the light. In the middle of the day photographers typically use a short shutter speed because there is a lot of light available to flow into the sensor. Towards sunset or sundown photographers tend to use longer shutter speeds because since there is not very much light available, the sensor takes longer to collect a sufficient amount of light to create an image.
On the new top performance digital slr cameras being released today, shutter speeds usually range between an incredible 1/8000th of a second and 30 seconds. There is also a “Bulb” function on most cameras that allows the photographer to just manually hold the shutter
open as long as he wants or needs to. Photographers typically only use the “Bulb” function when trying to take photos of lightning or fireworks. A shutter speed of 1/8000th of a second is short enough to freeze the motion of just about anything such as a batter hitting a fast ball or a race car sliding around a corner. A shutter speed of 30 seconds is long enough to collect sufficient light in almost in any situation such as a city street that is poorly lit or the inside of a room with only a few lights.
The aperture of a camera controls how much light is let into the sensor while the shutter is open. The aperture of a camera works much like the iris of an eyeball. In the bright of day the iris in our eyes contracts somewhat to minimize the amount of light that is let in to the deeper parts of our eyeballs. Aperture is the camera’s version of an iris and contracts or expands depending upon how much light the photographer wishes to have hit the image sensor.
Aperture is often much more confusing than shutter speed for most photographers because of how it is measured and it’s effect on a photo. Aperture is measured in something called f/stops. A very wide diameter aperture is f/2.8 and a very small diameter aperture is f/19. Lenses are rated and priced much on what apertures they are capable of achieving. Lenses that can achieve a wider aperture (lower f/stop) are said to be “faster lenses” and are therefore more expensive.
The relationship between shutter speed and aperture is the primary interaction that separates point-and-shoot photographers from advanced photographers. Advanced photographers usually pay careful attention to what aperture and shutter speeds they are using for each situation, point-and-shoot photographers couldn’t care less. Aperture interacts with shutter speed in a very precise manner. For example if there is only a little light available and you want to use a short shutter speed, then you will need a wide aperture to let more light in. On the contrary if you want to use a long shutter speed when there is only a small supply of light you will need a narrow aperture. But why would photographers care about what aperture they were using if there was a sufficient amount of light for any shutter speed? The answer is Depth of Field.
Depth of Field
In any given photo, there will be areas that are in focus and areas that are out of focus either in the foreground or in the background. Depth of field is the distance into the photo that everything stays in focus. The aperture is in direct control of how much depth of field will occur in a photo. A wider aperture (low f/stop) will create a small depth of field meaning that the subject will be in focus and not much else. A narrow aperture (high f/stop) will create a large depth of field meaning that almost the entire scene will be perfectly focused.
With a narrow aperture you must also consider that not much light is being let into the sensor therefore the shutter speed will have to be substantially longer. And since the shutter speed will need to be substantially longer it is probable that a tripod will be necessary. I almost always use a narrow aperture (high f/stop) for landscape photos and a wide aperture (low f/stop) for portrait photos.
Richard Schneider is a digital photography enthusiast and founder of http://www.picturecorrect.com/ which offers tips and news about digital photography, digital camera reviews, and photoshop tutorials. Please also visit http://www.picturecorrect.com/freewallpaper.htm where there is free high resolution desktop wallpaper available.
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