Practical Photography - UK (2019-09)

72 PracticalPhotograPhy

Do I focus through

the viewfinder

or in Live View?

I’ ve noticed that

when I focus in

Live View the

image is always sharp,

but I sometimes have

difficulty using my

viewfinder. Why is this?

Rachel Graves, Littlehampton

Ben says: a modern DSlr is

packed full of tech designed

to make the picture-taking

process as painless as

possible. two of the most

game-changing innovations

have been autofocus and

live View. the former makes

taking sharp pictures so much

easier, while the latter has

been a huge boon in aiding

exact composition. Much of

the time we take this tech for

granted, but sometimes it’s

useful to know what your

camera is doing...

Live View v finder

When you take a shot using

the traditional viewfinder

on a DSlr, most models will

autofocus using a system

called Phase Detection.

however, switching over

to live View also means

switching to contrast

Detection autofocus. the

reason for this is that contrast

detection can only function

when the image is being

projected onto the sensor.

Understanding which

system works best in which

conditions is thereforekey.

Phase or contrast?

Phase detection works by

using a pair of micro lensesto

compare and align the light

flowing through the lens.

it has some drawbacks, asit

is not possible to accurately

fo cus on the far edges of the

fr ame using this system.

additionally, it requires

critical alignment of the

micro lenses and the main

le ns, which in most DSlrs

allo w fine adjustment of the

autofocus system.

contrast detection works

by analysing the contrast

between pixels in real time,

with accurate focus being

achieved once a threshold is

reached.intheory,this isthe

moreaccuratesystem,as itis

based on the real scene.

Deciding which to use

will depend on the situation.

Phase detection (viewfinder)

isfasterandidealfornature

orsportsphotography,while

contrastdetection(liveView)

is more critical and better for

landscapes, but it is slower

and more prone to ‘hunting’.

Above & below Live View is veryusefulforcomposingyourshots,

but it is slower to focus, makingit unsuitableforactionphotography.

tip

aimfor

contrast

If youarehavingtrouble with
yourautofocus,lookfor an
areain yourscenewith
highcontrastand
fo custhere.

live view evf/viewfinder

tawatch ai1990

Valery Bareta