Photo Plus - UK (2020-01)

CUSTOM AUTOFOCUS

Make sure you focus after you zoom in order to avoid out-of-focus shots

The Canon Magazine 89

EOS S.O.S

You can customize AF-ON or AE

lock to give you the handy ‘back

button focusing’ feature

utofocus starts
when you press the
shutter release
button halfway and stops
when the camera has either
found something to focus
on (in One Shot AF), or when
you take your finger off the
shutter release button (in AI
Servo AF or Servo AF). Yo u r
camera may also keep focusing
the lens across a scene or
subject and eventually fail in
One Shot AF if there isn’t
enough light or contrast for it to
be able to detect an object.

In AI Focus AF, the autofocus

switches from One Shot to

Servo when it detects

movement, but for full control

it’s better to switch between

the two. Some cameras give

you the option of customizing

one of the buttons so it toggles

between One Shot and Servo

when pressed. This is ideal

when shooting a subject that

stops and starts, or gets

obscured behind objects, as

you can keep the camera set in

Servo mode and then lock the

focus at the touch of a button.

As well as

starting/stopping

AF, the shutter

button also operates

the camera’s metering system,

but you can separate these

functions via the Custom

Functions menu. Removing the

AF function means you can

avoid the camera refocusing if

you remove your finger from

the shutter button between

shots. The customization

varies: the EOS 5D Mark IV lets

you assign AF operation to a

number of different buttons.

lthough you can
focus more precisely
when you manually
select a single AF point, that
does require you to keep the
AF point on the subject.
That’s not always easy,
especially when you work with
small details. Long lenses, used
in breezy and cold conditions,
also increase the likelihood of
camera shake when you’re not
using a tripod. An IS lens can
help here, with the smoother
image in the viewfinder making
it easier to keep the AF point in
the right place.
Despite AI Servo AF being
the mode of choice for moving
objects, in some instances it
can be useful for shooting still
subjects. If you’re using One
Shot AF and you move the
camera back and forth even by
a small amount after the focus
has been locked, then that can
be enough to either make the
subject soft or blurred. But by
switching to AI Servo AF, the
camera will adjust the focus as
the camera moves.
Zooming the lens after
you’ve focused will normally
give you blurred results but,

again, AI Servo AF will

continuously focus as the lens

is zoomed in order to keep the

subject sharp.

If you customize the camera

as mentioned above, you can

leave it set to AI Servo AF and

then use another button to

start and stop AF. This gives

you the best of both:

continuous focus, then instant

‘One Shot’ when you need it.

This isn’t for everyone and it

takes getting used to after

years of conditioning to use

the shutter release button.

Activating AF

Sharper results

Customize the way that your EOS camera starts and stops focusing

Small adjustments can make a big difference

A

A

200 mm^

70 mm^