Amateur Photographer - UK (2020-03-28)

16 28 March 2020 I http://www.amateurphotographer.co.uk I subscribe 0330 333 1113

Technique

9

Aperture and AF points

When your DSLR camera focuses

using the AF system your lens is open at

the widest possible setting. For example if

you have a 24-70mm f/2.8 lens and your

camera’s aperture setting is set to f/8,

your camera will focus the scene at f/2.

and then switch the aperture to f/8 as the

shutter is pressed. Most cameras (with

the exception of a few advanced models)

need a minimum aperture setting of f/5.

in order for the camera’s AF system to

focus. For the majority of the time this

isn’t an issue, however it can become

problematic if you want to use a

teleconverter. For example if you have a

70-200mm f/4 lens and attach a 2x

teleconverter (which drops two stops of

light) this will drop your minimum

aperture setting to f/8. If you were using a

70-200mm f/2.8 with a 2x teleconverter

your minimum aperture would only

reduce down to f/5.6.

So really, faster

lenses are better

for a number of

reasons!

Mirrorless

cameras work

differently. They

don’t all necessarily

focus with the lens

wide open (some do,

but some use the taking aperture to

correct for any possible focus shift, and

others initially focus wide open then

fine-tune stopped down). They can also

usually autofocus at much smaller

effective apertures than DSLRs, so work

quite happily with teleconverters on

smaller-aperture telephotos. For

example Sony mirrorless cameras can

happily focus a 100-400mm f/4.5-5.

telezoom with a 2x converter attached.

8

Aperture and close-ups

As soon as you start looking at your subject

from a closer distance your aperture setting

behaviour changes. The closer you are to your

subject the more the depth of field drops. So

whereas before f/11 (on a full-frame sensor) was

the optimum setting for keeping the background

and foreground the same setting at a close

distance this aperture setting appears shallow. For

this reason many photographers ‘focus stack’ their

images, which in a nutshell is where they take

multiple images at different focus points and

process the images together for a sharp result.

6

Go wide!

Portrait and wedding photographers often use a

wide aperture to produce a dreamy and soft result. The

trick when using such a wide aperture setting is to

ensure you are spot on with your focusing (especially if

your subject is looking at the camera – focus on the

closest eye). For DSLR users make sure your focus is

set to a single AF point for pinpoint accuracy. For

mirrorless users you’re better off selecting Eye AF and

continuous AF, at which point the camera will find your

subject’s eye and hold it in focus as either you or they

move, which you inevitably both will. This lets you get

more consistently accurate results than with any DSLR,

especially when placing the subject off-centre.

If this type of effect is important to your style of

photography, invest in a camera that has a full-frame

sensor rather than a smaller one where the blurring

and softening effect is less effective.

7

Sensor size and aperture
The best aperture to use depends directly on your
camera’s sensor size. A lot of the advice you read online
or in magazines is written from the perspective of
full-frame users. Telling people to stop down to f/11 for
depth of field is good for full-frame, but bad news for
Micro Four Thirds as you’ll get unnecessarily soft results
caused by diffraction. Instead Micro Four Thirds should
use f/5.6 to get the same effect as those shooting on a
full frame at f/11. For any given angle of view, focus
distance and f-number, with smaller sensors you get
increased depth of field, along with increased visibility of
diffraction softening.
Here’s another example: f/8 on a full-frame camera
equates to f/5.6 on APS-C (1.5x crop factor), f/4 on
Micro Four Thirds (2x crop factor), f/2.8 on 1-inch-
sensor compacts (2.7x crop factor) all to a close
approximation. As a result, the smaller the sensor, the
wider the apertures you should use for best results.

A lot of wedding

photographers use a

wide aperture setting

to create dreamy and

atmospheric results

The closer you get

to your subject the

more your depth

of field drops

Always take

into account

lens length

with aperture

choice...