14 28 March 2020 I http://www.amateurphotographer.co.uk I subscribe 0330 333 1113
Technique APERTURE ESSENTIALS
All about
aperture
Newer camera tech means old aperture ‘rules’ may no
longer apply. Claire Gillo has more up-to-date tips
1
The basics
Aperture derives from the Latin
word apertura, and is defined as a hole
or a gap. It controls how much light
you let through your lens to the
camera’s sensor. The amount of light
that enters is measured through a
system called f stops. By increasing or
decreasing the size of the aperture
diaphragm it will affect the depth of
field in your image. The depth of field is
how much of the image is sharp in
front of and behind the selected focus
point. Other factors contribute to the
depth of field too, such as the focal
length of the lens, and the camera-to-
subject distance; we’ll get to that later.2
Why the f do we use f-stops?
When you start learning about the
exposure triangle it’s easy to get your head
around shutter speed and ISO as they follow a
basic numbering system. The aperture f-stop
system seems like a random arrangement of
numbers, but hang on there is logic. The
f-number is the ratio of the lens’s focal length (f
stands for focal length) to the diameter of the
aperture hole. So if you had an aperture of f/
on a 50mm lens to find the width of the
aperture hole you divide 50 by 4, giving a
12.5mm diameter. For an f/8 aperture on a
50mm lens the aperture hole is 6.25mm. So
the higher the f-stop number the smaller the
aperture hole as you have a larger number to
divide the focal length by, and vice versa.3
Distance and aperture
We all know that if we stop down to a narrower
aperture number that our depth of field will increase;
and if we open it up wider, the depth of field will be
less. However, there are other factors at play here- with the distance between you and your subject,
and your subject to the background as one of them.
For example if you position your subject away from
the background, and set your aperture to f/4, your
subject will be sharp and the background blurred.
But if you ask your subject to stand closer to the
background and take the same shot at the same
setting the background will become less blurred.
Think about your subject’s positioning in the scene, to
get what you want from your aperture. A handy app
you might want to download onto your phone is a
Depth of Field calculator. There are many free ones.
Claire Gillo
Claire Gillo is a photographer and writer living in
Devon. She writes articles for a number of
photography publications including Amateur
Photographer and Digital Camera. Find out more
at http://www.clairegillo.com or follow her on
Instagram @clairegillophotography.