Practical Artistry: Light & Exposure for Digital Photographers

14 Understanding Exposure

What Is an Exposure?

What Is an Exposure?

The word exposure can be used to mean a number of

different things. It’s important to be clear about these

meanings. After all, exposure is part of the title of this

book.

An exposure can mean a photograph, as in “I’ve got 100

exposures on my memory card.” The word can also be

used to refer to a finished photographic print or image

on the Web: “Wow! That’s a nice exposure.”

More relevant to the content of this book, an exposure

can also mean the amount, or the act, of light hitting

a sensor. Finally, and most importantly, an exposure

can also mean the camera settings used to record this

incoming light.

With exposure used in the last sense, and given a par

-

ticular camera and lens, there are three settings (and

only three settings) that can be used to make an expo-

s

ure: shutter speed, lens aperture, and light sensitivity

(also called ISO).

Consider that a camera is a light-proof box with a lens

attached to an opening in the box, and a mechanism

for recording exposures inside the box. This is fun-

d

amentally unchanged since the early days of analog

photography. So are two of the three settings that make

an exposure: shutter speed and aperture.

Shutter speed m

eans the duration of time the camera

is open to receive incoming light, and, as a result, the

15

Understanding Exposure

Lying flat on my belly, I photographed ...