Photography
Author:Joseph LaForest, University of Georgia
Basic camera terminology
- Focal length
- This is measured in millimeters (mm). Technically, it is the distance from the center of the lens to the film or sensor of the camera. Practically, this directly affects the angle of view. The longer focal length, the narrower the angle of view and the more distant objects are magnified.
- Shutter speed
- The length of time that the shutter stays open when taking a photograph. The key to understanding shutter speed settings is knowing that the numbers on the camera are the bottom of a fraction (i.e. 1/x). A shutter speed of 250 means 1/250th of a second. The larger the number for shutter speed, the "faster" the shutter speed and the less time that the film or sensor is exposed to light. When trying to take clear, non-blurry images, the "slowest" shutter speed that can be use when holding the camera (as opposed to a tripod) is around 60 (1/60 of a second). Cameras equipped with vibration reduction can help when taking images at low shutter speeds.
- Aperture
- Technically, the size of the hole that light passes through when taking a photo. This is also referred to as the f-number (e.g. f/5, f/32). Practically, affects the "depth of field" (how much of the subject is in focus) and the amount of light that reaches the film or sensor or the camera. Like shutter speed, aperture is also a little counter intuitive; small f-numbers mean big apertures and large f-numbers mean small apertures.
- ISO
- Film speed. Practically, this is how sensitive the film or sensor is to light. The higher the ISO, the more sensitive the film or sensor. Increasing the light sensitivity (selecting a higher ISO) can be very useful in low-light conditions, however, the higher the ISO the more "grainy" the image will be and fine detail may be lost.
What does it take to make an image?
Cameras have a light sensitive surface that is either film or an electronic sensor. To create an image, the film or sensor has to be exposed to a certain amount of light as determined by its ISO (light sensitivity). The photographer choose the aperture and shutter speed which determines how much light is allowed to hit the film or sensor and the amount of time it is exposed to that light.
To help visualize this, imagine that you are given the job of filling a bucket with water. You can choose how big of a spigot (aperture; f-number) and how long you leave it open (shutter speed). If you choose a big spigot (big aperture; low f-number) you do not have to leave it open very long to fill the bucket. You can also fill the same bucket with a tiny spigot (small aperture; high f-number) but it will have to stay open much longer. Improper selection results in either partially filled buckets (underexposed images) or overflowing the bucket (overexposed images).
After you have this initial analogy down, you can begin to think of the amount of light in the room as the water pressure supplying your faucet. In a dim room (low water pressure), having the aperture wide open (big spigot) will still require you to have a slower shutter speed (longer wait for the bucket to fill), compared to taking a the same photo with the lights on (high water pressure).
Taking images based on depth of field
In many cases, effective use of depth of field (i.e. how much of an image is in focus) is the primary concern of the photographer. A shallow depth of field can be used to blur the background to keep emphasis on the main subject of the image. In other cases, such as in macrophotography, a deep depth of field is needed to capture all the detail of a small object.
Depth of field is controlled by the aperture setting of the camera. A higher f-number is used to get a greater the depth of field, but since this setting results in a small aperture, less light reaches the film or sensor. Using a higher f-number will require the photographer to either:
- decrease the shutter speed (i.e. leave the shutter open longer) or
- increase the amount of light by using a flash or additional light source.
When additional light sources are not available and the exposure time would be slower than 1/60th of a second, a tripod or copy stand can be used to stabilize the camera during the longer exposure. This also means that the subject cannot move while the photo is being taken. Wind and other environmental factors can make this very difficult as can living subjects.
Flash units can easily be used to provide extra light and allow the photographer to use faster shutter speeds. Using this technique, it is possible to make the background appear empty since only on the main subject is provided additional light and there is insufficient light to produce an image of the objects in the background.
