Photo Plus - UK (2019-09)

FOCUS FIXES

The Canon Magazine 87

EOS S.O.S

Tips for accurate focus with limited depth of field

F

Ask Brian!

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your Canon DSLR?

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ast aperture lenses help to
create images with limited
depth of field, and are ideal for
when you want to separate your subject
from their surroundings. Fast lenses
don’t have to be expensive – the
fabulous EF 50mm f/1.8 STM lens is
one of the cheapest lenses in Canon’s
range. To get great results with wide-
open apertures it’s important that the
photo has some elements that are
critically sharp, and others that are
significantly out of focus for contrast.
Instead of letting the camera select the
AF point automatically, it is best to use
a single AF point so that you control
where the point of focus is precisely.
Cameras choose the closest subject
if you let them select the AF point for

you. If your camera has spot focus

point or smaller AF frame size then

use these for the utmost precision.

If you use the central AF point, then

focus, hold the shutter half-pressed to

lock AF and recompose then the small

change in distance sometimes results

in the focus being off. It’s better to

select a single AF point that is closest

to the part of your subject you want

sharp, which usually means moving

the AF point away from the centre.

Just because you have a fast lens,

it is not always necessary to shoot

wide-open. Stopping down from f/1.8

to f/2.5 still gives a shallow depth of

field but with a little more room for

error. The further you are from

the subject, the more depth of field you

have even with the aperture wide open.

Longer focal lengths are ideal for

portraits as they flatter facial features.

The final step is to make sure the

shutter speed is fast enough. With very

limited depth of field the slightest

movement of the subject can mean

they’re out of focus or blurred. This

slight out of focus result is more

obvious as so little in the frame is

sharp when shooting wide open.

Thankfully shooting wide open lets

plenty of light in to the camera to help

keep shutter speeds high. Using a flash

can also help out here, as the short

duration of a flash freezes the subject

and keeps in-focus elements really

sharp. Lots of practice really helps

to guarantee results.

A fast f/2.2 aperture separates the lead rider

from the field, and a 1/1000 sec shutter

speed ensures they are frozen

Contrast between in and out of focus

elements in the frame is accentuated

by the wide-open f/1.2 aperture and

precise focus on the eyes

Accurate focus

for fast lenses