Digital SLR Photography - UK (2019-12)

CUT THROUGH THE JARGON AND THE CONFUSING MATHEMATICS TO

BREAK DOWN THE BASICS OF APERTURES AND HOW BEST TO USE THEM

APERTURES EXPLAINED

48 Digital SLR Photography December 2019

AS WE ALL KNOW, photography at its core is

the capture of light through a lens, whether

that's using an imaging sensor or on film, via

a smartphone, a compact camera, CSC or

DSLR, the principle is the same. Obviously

there's a lot more involved in creating brilliant

photographs – otherwise we would all be

producing award-winning pictures and you

wouldn't be enjoying this magazine – but at

its foundations, every photographic journey

begins by asking one question: How do you

control the light that enters the lens that

creates the image? Auto modes do a sterling

job of taking the thought out of answering

this question, but anyone reading this wants

to be more than a button-pusher; they want

to be a photographer, and thoroughly

knowing the answer is your first step.

Every lens – bar the most basic types – has

an iris (also known as a diaphragm) that opens

and closes to varying degrees to allow light to

pass through and reach the sensor. Add in

your shutter speed, which controls how long

the shutter stays open and the ISO rating that

determines the sensitivity of the sensor to

light, and you’ve the recipe for exposure.

The size of the aperture is referred to in f/

stops (f/1.4, f/5.6, f/16, and so on). The lower

the number (e.g. f/1.4); the wider the opening

and the more light that can pass through.

The higher the number (e.g. f/16) the smaller

the opening and the less light passing

through. It sounds contradictory, as we

instinctively think f/8 will be larger than f/4,

for instance, but with practice picking the

right aperture becomes second-nature.

While the amount of light reaching the

sensor has an obvious impact on your

image’s exposure, your aperture is also what

controls depth-of-field: the depth of

sharpness in your image. It’s why you might

hear landscape photographers talk about

using mid to small apertures, such as f/11 or

f/16, for front-to-back focus or portrait

photographers who embrace the blur

shooting wide open at f/2.8. The wider the

aperture, the shallower the depth-of-field;

the smaller the aperture, the sharper the

scene is from foreground to background.

(Turn the page for more details on how to

control depth-of-field).

The effect your aperture choice has on

your shutter speed is worth noting, too. To

get a ‘correct’ exposure, when working in

aperture-priority mode, your camera will

adjust your shutter speed to balance with any

changes in aperture to retain what it deems

to be a ‘correct’ exposure. For instance,

there’s one full stop’s difference between

f/2.8 and f/4, so if you close your aperture

down by one stop your camera will lengthen

your shutter speed by an equal amount to

stop your image from underexposing. If

you’re working with a stationary subject or a

tripod, this may rarely be a problem, but it’s

certainly a consideration to keep at the

forefront of your mind if you’re handholding

your camera or have a moving subject: one

stop of light can mean the difference

between 1/60sec and 1/30sec, for instance,

or a sharp or possibly soft handheld image.

Conversely, if you need a faster shutter speed

you can open the aperture up from, say, f/4

to f/2.8, to automatically shorten the shutter

speed. Alternatively you could also factor in

the third point in the exposure triangle – the

ISO. By doubling the ISO from 200 to 400,

for instance, your sensor will be twice as

sensitive to the light received, which is the

same as opening up the aperture by a stop or

slowing the shutter speed. For example, if

you started with an exposure of 1/250sec at

f/5.6 (ISO 100) but want more depth-of-field

by closing your aperture to f/8, increasing

your ISO from 100 to 200 will stop your

camera from slowing its shutter speed from

1/250sec to 1/125sec and still retain the

original exposure. There comes a point,

SELECTING YOUR APERTURE: THE CORE FOUR EXPOSURE MODES

Above: Using the right aperture and lens combination to

suitthesubjectandscenewilldeliververyattractiveresults.

Photo Masterclass

APERTURE-PRIORITY MODE (A/AV):

In A/AV mode, you select the aperture and

your camera chooses the shutter speed.

Unless you have set Auto ISO, you control

the ISO rating too. You can use exposure

compensation to override your camera’s

chosen exposure, if necessary.

S HUTTER-PRIORITY MODE (S/TV):

Yo u s e le c t t h e s h u t te r s p e e d a n d ISO

rating, while your camera selects the right

aperture for a correct exposure. You can

use exposure compensation to override

your camera’s chosen exposure, but

you've little control over depth-of-field.

MANUAL MODE (M): Youselectthe

shutter speed, ISO and aperture;giving

you the ultimate control overyour

exposure. In theory, you canpickthebest

aperture for depth-of-field andthe

necessary shutter speed, andusetheISO

rating to refine the exposure.

P ROGRAM MODE (P): This fully

automated exposure mode chooses the

shutter speed and aperture combination,

but gives you power over White Balance

and ISO rating. Use the camera's input dial

to 'shift' the exposure to alter the selected

aperture and shutter speed combination.

however, when using your ISO rating does

more harm than good as you can begin to

introduce hot pixels and quality-degrading

noise into an image; this is usually around

ISO 800, but it differs for every camera.

Now you’ve grasped the basics, let’s see

how the best practice for apertures differs

depending on your subject matter and lens

type. Ever wonder what the best aperture is

for landscapes (p52), portraits (p54) or nature

(p56)? What about for hyperfocal distance or

minimal depth-of-field? Let's find out...