INTRODUCTION

EXPOSURE

Definition: The camera and lens settings that determine the amount and qualities of light falling on the medium used to record the image. Traditionally shutter speed, aperture, and ISO with film, but the digital age expands this list to include in-camera adjustments that determine how the exposure data is interpreted: color space, white balance, dynamic range, sharpness, noise, filter effects, and more.

Perhaps the first issue to clarify in this book is the difference between the terms "exposure" and "metering." Exposure is a term that describes the actual settings used to capture an image, whereas metering provides only a suggested group of settings that you are free to ignore, override, or adjust as you see fit. It is vital to remember that in-camera metering systems, which many of us rely on quite extensively, may have grown extremely sophisticated, but they are not absolutely perfect for every situation.

The second important point relates to which file format you use to record your images, provided your camera offers both RAW and JPEG options. If you want to print images directly from your memory card, for example, you will need to record images using the JPEG format and you will need to have exposed them with a fair degree of accuracy. However, if you are comfortable with adjusting images on your computer before printing (generally referred to as post-processing), you have a little more leeway with the exposure. This is especially true if you are recording your images as RAW files, as these allow you to adjust almost all of the original camera settings during post-processing, including the exposure.

The three main settings at the heart of exposure are aperture, shutter speed, and ISO. Virtually every camera offers at least one fully automatic mode in which the camera sets all three of these for you. Most will also provide a number of fully or largely automatic modes often referred to as "scene modes" that will also determine the aperture, shutter speed, and ISO automatically, but based on the subject matter of the image or the type of circumstances in which the photograph will be captured. Before we examine their relationship in greater detail, let's first look at these three settings individually.

Aperture

The word aperture means an opening through which something passes, and in this context we are talking about an opening within a camera's lens through which light passes (the mechanics of which are described more fully in Chapter 3).

The light waves project an image onto the film or sensor, with the size of the aperture controlling the amount of light that is allowed through. This obviously has an impact on the brightness of the resulting image.

If you peer into any lens from a camera that takes interchangeable lenses you will clearly see this opening, formed in the center of a number of overlapping blades. The shape of this can be (but usually isn't) a perfect circle.

When we talk about the aperture used for a particular photograph, we are really talking about the size of the opening and, in order to be precise, we refer to it numerically, as a fraction of the focal length. The number used is preceded by a lower-case letter f, sometimes italicized and followed by a slash; for example, f/8. The actual range of numbers used will be explained shortly.

Shutter speed

The shutter speed refers to the amount of time that the light waves passing through the aperture are allowed to fall on the recording medium, be it film or the sensor in a digital camera. There are several types of shutter mechanism (descriptions of which would cloud the issue at this point), so at this stage it is only necessary to appreciate that the shutter offers another mechanism for controlling light, in this case the duration that light waves are allowed to form an image on the recording medium. This is always expressed as whole minutes, whole seconds, or a fraction of a second (1/500 sec., for example).

ISO setting

The ISO setting refers to the sensitivity to light of the recording medium and is expressed numerically; ISO 200, for example. One disadvantage of film is that a constant ISO has to be applied to every frame on the roll of film, whereas with digital cameras the ISO setting can be changed for individual photographs. The acronym ISO stands for International Organization for Standardization, the body responsible for setting regulations that all manufacturers must adhere to.

Stops

A stop is the term used by photographers to describe the doubling or halving of the light received by the recording medium. This means that the term can be used in conjunction with any of the three main settings concerning light: aperture, shutter speed, or ISO. Usually we refer to 1 stop faster, meaning a halving of the light received by the recording medium, or 1 stop slower, meaning twice as much light being received. (It is important to understand that the terms faster and slower in this context do not relate only to shutter speed.)

Summary

The easiest analogy to draw when it comes to the relationship between the aperture and shutter speed is that of cooking a meal in the oven: You can opt for two hours at 150° or one hour at 300° and the outcome will be largely the same. Think of these as being the shutter speed and aperture. Continuing this analogy, you have a third factor that can also affect the outcome — the height of the oven shelf. This equates to the ISO speed. OK, so my cooking skills fall a little short of any photographic expertise I may possess, but you get the idea: the key to exposure is getting the correct balance between these three variables.

A simple way of witnessing the relationship between the shutter speed and aperture is to set your camera to Program mode. If you shift the exposure, you will see that the camera scrolls through a variety of different combinations, each of which will give the same overall result at the selected ISO speed.

Camera modes

The technological rollercoaster that has hurtled through camera development at breakneck speed throughout the last decade should have made life easier. It did, for a while, but even inexpensive compact digital cameras now offer a huge range of settings options. There is much to explore, to learn, and to experiment with these days, but most of the technology can be broken down into several topics that are outlined here and explained in greater detail later in this guide.

Primary and secondary exposure

The terms primary and secondary exposure are not standard terminology, but they have been used here to separate the adjustments made in-camera at the time of shooting from post-capture corrections.

Primary exposure settings are the ones that you will use in-camera when you capture an image. They incorporate the main settings of ISO, aperture, shutter speed, exposure compensation, exposure bracketing, Highlight Tone...