Australian Camera — May-June 2017

T

ranslated from Greek, the

word photography means

‘drawing with light’ and

the essence of creating

a photographic image lies with

controlling exactly how much light

reaches the recording medium,

whether it’s a digital imaging

sensor or a frame of fi lm. Logically,

this is called an ‘exposure’

(i.e. the recording medium is

exposed to light) and in any

camera, it’s essentially regulated

by two controls – apertures and

shutter speeds. As explained

in the previous article about

depth-of-fi eld (see our January/

February 2017 issue), the aperture

mechanism – also known as the

diaphragm – is located within a

lens and comprises a set of blades

which move to create openings of

different sizes. This allows more,

or less, light to pass through to

the image sensor, and their sizes

(in other words, the diameter) are

expressed in values called ‘f-stops’.

An f-stop is written as the letter ‘f’

followed by a number... i.e. f4.0.

These numbers are determined by

a simple equation; the focal length

of the lens divided by the diameter

of the aperture. This results in a

numbering sequence which is

the opposite to what would seem

logical... so the larger apertures

have smaller f-numbers and the

smaller apertures have larger

f-numbers.

In practice then, a lens might

have an aperture range from, say,

f2.8 – its very largest or widest

aperture – to f22 – which is its

smallest aperture setting.

As the diaphragm progressively

closes down, each aperture setting

• which represents one f-stop
  of adjustment – actually lets in

half the amount of light as the

previous one.

Stops And Speeds

You can think of a ‘stop’ as the

unit which applies to any exposure

adjustment. Shutter speeds are

also adjusted in stops, and the

doubling or halving relationship

between settings again applies.

While the aperture controls the

amount of light coming through

the lens, the shutter regulates how

long the sensor is exposed to it...

i.e. the duration of the exposure.

This is done by opening the shutter

ALL ABOUT EXPOSURE CONTROL

72

BACK TO BASICS

Controlling exposure is a fundamental of photography, but if you leave it

entirely to the camera, you’re missing out on some vital creative possibilities.

Here’s what you need to know to access some powerful pictorial tools.

PART 1

CamMayJune17_072-074 BacktoBasics.indd 72 13/04/2017 12:16 AM