Exposure and Focus

Color balance and latitude are two important characteristics of film and
digital media. Color balance is the film or CCD’s response to colors in a
scene. Latitude is the amount film or a CCD can be under- or overexposed
and still deliver a decent picture. Digital cameras are capable of
overexposure and underexposure but actually have no more latitude
than print film! For this reason, your images must be technically accurate
for both types of media.
By comparing film and film technologies to the capabilities of digital
cameras, you will certainly learn new techniques to try in digital. This
chapter explains color balance and then examines the capability of both
mediums to handle extreme exposure situations.

Digital Cameras and Color Balance
Digital cameras are not immune to color balance issues, although white-balance
features in most cameras help to reduce problems when used properly. White-balance
enables photographers to set the “white point” for a camera before pictures are
taken. This forces a camera to consider a specific color of lighting as purely white
light.
The purpose of a white point (white balance) is to force the camera sensor to see the
color you designate as pure white. To avoid off-color images taken indoors with fluorescent
bulbs or zenon bulbs, you might need to point the camera at a white object
(such as a piece of cardboard or a white wall), and then set the white balance on the
camera. By setting a white point, the camera will not have color-cast issues later on.
Television news crews, for example, avoid strange colors and skin tones by setting
the white point of their video cameras prior to every shoot.
Most digital cameras can accurately compensate for lighting color and overcome
unusual lighting conditions. However, occasionally their automatic adjustment systems
get confused. This often happens indoors, where lighting systems can vary
greatly. If you’re shooting indoors under unusual lighting, set the white balance on
the camera before taking pictures.
To set the white balance for your camera, follow these general steps:
1. Access the menu on your camera. Usually there is a dedicated Menu button
somewhere on the back of the camera.
2. Scroll through the menus until you find a setting for WB, White Bal, or White
Balance.
3. There might be a few more choices, such as Presets. Continue through the
menus until you reach choices that resemble the following:
■ Auto. Automatically corrects white balance. This setting is often the
only one you need, especially if you photograph outdoors.
■ Daylight. Set the white balance to daylight if you’re shooting outside.
■ Tungsten. Set white balance to tungsten, if you’re shooting indoors
with incandescent bulbs (the screw-in type from GE). These bulbs emit a
lot of yellow light. The tungsten setting will compensate by reducing
yellow and increasing blue.
■ Fluorescent. Set to fluorescent to compensate for the excessive green
output by these tubes.
4. Highlight one of these choices and then press OK. The camera is ready for
unusual lighting.
The color temperature of “white light” is measured on the Kelvin scale . Warm colors of light have low color temperatures; cool colors of light have highcolor temperatures.
Different color films are manufactured for different color temperatures. Daylight film
is balanced for 5,600° Kelvin (or K) light and gives accurate color with midday sunlight
or electronic flash. Indoor film, called Type B or tungsten film, is balanced for
3,200°K light and gives excellent color with professional quartz-halogen lights (powerful
lights up to 1,000 watts). It will give acceptable, slightly warm color with ordinary
incandescent light bulbs, which are 2,500°K to 2,800°K.
Video cameras and some digital cameras have circuitry to automatically adjust the
color balance to match the color of the light source. Digital cameras also provide settings
that enable you to emulate the warm yellow cast of indoor lighting or the
harsh green color common with fluorescent lights. These custom settings resemble
different types of film such as tungsten and indoor film.