Learn how (and why) things work

By Bradley Wilson ©2006

Focus

Just like your own eyes, camera lenses focus on one plane parallel to the “film” plane. Images not on that plane appear out of focus. All images need something in focus – the subject of the picture. Practice focusing. Don’t let the camera always focus for you.

International Standards Organization for (ISO)

The International Standards Organization value is the sensitivity of the film or digital chip to light, and can be referred to as ISO, ASA or DIN. Films with a lower ISO number such as 64 or 200 indicate less sensitivity to light. High ISO speeds (800 or 1600, for example) indicate more sensitivity to light. Lower ISO films tend to have better color and less grain, so they tend to look better and when enlarged, show less grain. Higher ISO films tend to be more grainy and have lower color quality but allow for shooting in lower light situations with faster shutter speeds.

f/Stops

F/stops are measures of aperture size, the opening in the lens through which light passes. Each f/stop is half as much light as the f/stop preceding it, or twice as much as the f/stop it precedes. For example, f/4 lets in half as much light as f/2.8 and twice as much as f/5.6.

Shutter Speeds

The other factor that controls how much light reaches the film plane is the shutter speed, the amount of time that the film, or digital chip, is exposed to light. Shutter speeds are measured in fractions of a second. A shutter speed of “60” is actually a 1/60th of a second exposure. Slower shutter speeds allow more light and are used for shooting in lower light or night time. Faster shutter speeds allow less light and require a lot of light but can stop action.

Exposures

An exposure is defined by the f/stop and shutter speed values at a given ISO. To allow for a longer shutter speed, allow less light to the film by choosing a smaller aperture. To shorten the shutter speed, allow more light to hit the film by using a larger aperture.

The light meter on the camera gives an initial exposure reading based on what it sees. For example, you may be out shooting intramural lacrosse and the meter reading says f/8 at 1/250. You know, however, that all the poles and people in the background are distracting, so using low depth-of-field will be critical and f/8 is pretty high. You also know that stopping the fast action will be important. So, if you go down to f/5.6 (one MORE stop of light), the picture would be overexposed if you didn’t also go up to 1/500 (one LESS stop). Now, you’re meeting both goals, using a faster shutter speed to stop the action and a lower aperture to get lower depth of field. In fact, you can continue in this trend until you reach f/2.8 @1/2000, minimizing the depth of field and the shutter speed. All of these exposures are equivalent, letting in the same amount of light.

Don’t solely rely on your camera’s meter for exposure. Meters can easily be tricked, especially when there is a great deal of light or dark area in the scene.

Also, learn your camera’s metering modes: spot metering, center-weighted metering and average. They are all useful for different types of scenes.

Depth of Field

The depth of field is what is in focus beyond the exact plane of focus. In short, the depth of field is the area in front of and behind the subject on which the lens is focused that appears in focus. Three factors influence depth of field.

1. F/stop — Larger apertures (with smaller numbers such as f/2.8 or f/2) have lower depth of field — less appears in focus. Smaller f/stops (with larger numbers such as f/16 or f/22) have higher depth of field – more appears in focus.
2. The distance from the camera to the subject — The further away the subject is from the camera, inherently the more of the image appears in focus.
3. Lens length — The smaller the focal length, all other things being equal, the higher the depth of field. More of an image will appear in focus with a wide-angle lens than with a telephoto lens at the same distance and f/stop.

Lens Focal Legnth

Each lens has a focal length measured in millimeters. Shorter length lenses, less than 50mm, are considered wide angle lenses. They allow the camera to see a wider area than the human eye. Some lenses become so wide that they begin to distort lines in the image from straight to curved. These lenses, often with an angle of view of 15? or more, are called fisheyes and can sometimes capture an image at almost 180?. Normal lenses are lenses that see at about the same angle as the human eye, about 50mm. Telephoto lenses see at a smaller angle than the human eye and therefore capture less of the scene, magnifying the image. A 300mm lens will appear as if you are looking through a small telescope.

White Balance

In the days of color film photographers used filters for different kinds of light. All light sources have a different temperature. Just like sunshine appears white, tungsten light (conventional light bulbs) appears orange and fluorescent light appears blue. Digital cameras now have a white balance function that must be set depending on the source of light. Some of the most common temperatures are for tungsten, or the common light bulb, flash, fluorescent and sunshine.