Basic exposure 37
Light and color
Light is made up of all colors in the spectrum. We see the color
in objects because as the light falls on the object, it is refl ected
back to us and onto the camera’s sensor at the time of exposure.
Objects are colored because they absorb different portions of the
spectrum. A piece of red paper is red because it refl ects red light
even though the white light falling on it consists of red, green,
and blue. The green and blue are absorbed by the paper, leaving
only red.
Metering devices measure light using two different methods:
refl ected or incident. Both techniques let us know the best expo-
sure that averages the tonal range in the scene based on the
mid-tone being the standard 18 percent gray. In-camera meters
take a refl ected light reading by measuring the light that is being
refl ected off the subject. It will not surprise you to learn that
white or very light objects refl ect more light than do black or
dark objects. In the middle of summer in the desert, would you
rather wear a white shirt or a black shirt to protect you from the
sun’s rays? Because black absorbs most of the light and converts
it to heat, you’d do better with the white shirt, which refl ects
more of the light back into the air so you can stay cooler.
If the scene being measured is average in terms of light values,
having no really large bright or dark areas, the camera meter’s
job is quite easy. If something in the scene refl ects lots of light—
for example, from a snow-covered hill, the ocean and sand at
the beach, or a shiny metal object—the meter adjusts for this
extra brightness and tells the camera to allow a smaller amount
of light onto the image sensor. In this situation, the typical pho-
tograph does not receive enough exposure, and the images turn
out darker than the original scene appeared to our eyes. On the
other hand, should there be a large portion of the image with low
light values—the darkened stage with someone in spotlight,
mountains in silhouette at sunset, eight groomsmen in black
tuxedos surrounding the bride for a formal wedding portrait—
the meter adjusts for the darkness, sending more light to the
sensor, overexposing the photograph.
The good news is that today’s in-camera meters are very good at
sensing those extreme hot spots or dark areas. We also have the
ability to instantly view our images on the digital camera’s LCD
screen and make adjustments on the spot. Remember, however,
that in many documentary, sports, or photojournalistic situations,
even this instant image review isn’t quick enough—decisive
moments come and go in split seconds and can’t be restaged.
More importantly, we have the histogram to view for precise
exposure evaluation. Barry learned the hard way that the image
on the LCD screen can be misleading, and he’s now an ardent
believer in using the histogram to check exposure accuracy.
