Aperture-Priority AE Technique #1: The Relationship Between Lens Aperture and Bokeh
Not many people know this, but one of the benefits of the larger image sensor on your camera is that it helps to enhance that beautiful out-of-focus effect known as "bokeh". You can use this effect to separate a subject from its background and make it "pop". How do you do it? Read on to find out more! (Reported by: Teppei Kohno)
i) What is aperture and how does it relate to bokeh?
ii) How do I control the aperture?
iii) Telling the maximum aperture from the lens name
iv) Step-by step: Changing the aperture setting
v) Bonus tip for enhancing flower photos
Here's a quick recap: Aperture refers to the opening in your lens that allows light to enter the camera. This opening is formed by aperture blades.
The size of this opening affects the "depth-of-field", which is the area of the image that appears in focus. The area outside this (the "out-of-focus area") is blurred in a way that looks different from motion blur or camera shake. This quality of blutting is what we know as "bokeh".
Here is how they are related:
- - Larger opening = shallower depth-of-field = stronger bokeh
- - Smaller opening = larger depth-of-field = less obvious bokeh
There are actually four factors that affect bokeh and depth-of-field. (Learn about them in Lens Basics #3: Creating Bokeh). However, the easiest way to create bokeh is to control the aperture, which is the focus of this article.
Aperture is expressed by a figure known as the f-number. A smaller f-number refers to a larger aperture opening.
On your camera, you control the size of the opening by changing the aperture setting (aperture value/f-number) on your camera. (Here’s a step-by-step guide on how to do it.)
I tried to change the f-number but can’t. Why?
This is probably because you are using the wrong shooting mode. You can only control the f-number if you are using either of the following modes:
- - Aperture-priority AE (Av) mode
- - Manual (M) mode
- - Flexible-priority AE (Fv) mode (if your camera has it)
While you can also get very pretty pictures with Program AE (P) mode or the Special Scene modes, in these modes, the camera decides on all the exposure settings including aperture, and you cannot change them. This means that it’s harder to get the bokeh effect to look the way that you want.
I'm a beginner. Which mode should I start with?
In the shots below, the f/2.8 example was shot in Av mode, while the f/8 example was taken using the P mode. Notice the difference?
Av mode - f/2.8
The flower stands out with a lovely bokeh effect in the background.
P mode - f/8
The camera set a relatively narrow aperture of f/8 because of the bright sunlight. While the exposure is perfect, the bokeh effect is not as nice and creamy as the f/2.8 example. There is still a bit of bokeh effect because I was shooting so close to the flower, but the f-number makes a huge difference.
Every lens has a different maximum aperture This is usually stated in the lens name in the numerical portion that starts with "f" (in the red box below).
Why do some lens names state a range of f-numbers?
On a variable aperture zoom lens such as the EF-S18-55mm f/4-5.6 IS STM, the maximum aperture changes depending on the focal length you use. In this case, two f-numbers are stated in the lens name. The first number is the maximum aperture at the wide-angle end, and the second number is the maximum aperture at the telephoto end.
For example, this is what the name "EF-S18-55mm f/4-5.6 IS STM" tells us about the smallest f-number that we can set:
- - At focal length 18mm, it is f/4
- - At 55mm, it is f/5.6
- - At the focal lengths in between, it is between f/4 and f/5.6
The name of the lens may also be stated on the front of the lens.
Try changing the Picture Style to make the colours of the flowers appear more beautiful. Setting the Picture Style to "Portrait" mode increases the vividness of the pinks and yellows of the flowers.
"Standard" Picture Style
The picture looks fairly vivid and lively but there is still something lacking.
"Portrait" Picture Style
In this shot, the colours are more intense.
Learn more about how to use Picture Style to change the look of your shots in:
3 Steps to Creating Custom Photos With Picture Style
EOS M6: Three Features You Can Use to Achieve Stunning Shots of Night Cityscapes
Night Photography: Adjusting Contrast for a Picturesque, Surreal-looking Image
*Images are for illustration only. Your camera’s dials and buttons may look slightly different!
1. Set the camera to [Av] mode
Turn [ON] the power supply and adjust the Mode Dial to the [Av] mode.
Know this: Some cameras like the EOS M6 Mark II come with the Fv mode, which works like the P mode except that you can easily override any of the camera-defined exposure settings when you want. It's convenient for when you're mostly happy to let the camera decide, but occasionally want to take back control!
2. Turn the Main Dial
Turn the Main Dial with your index finger to change the f-number. Turn the dial to the left to reduce the f-number and approach the maximum aperture. Turn the dial to the right to increase the f-number.
3. Check that the f-number has changed
On rear LCD screen during OVF shooting on a DSLR
During Live View/EVF shooting
The current f-number will appear as circled. Check that the f-number has changed before taking the picture.
In upcoming articles, we will explore different f-numbers and how they are good for achieving different effects. In the meantime, how about taking some shots with different f-numbers and seeing how it changes the look of your bokeh? If you want to shake things up, try varying the other factors that create bokeh too.
Have you shot any images with bokeh lately? Share them with us on My Canon Story, and you might just end up inspiring others!
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Born in Tokyo in 1976, Kohno graduated with a Social Work degree from the Department of Sociology of Meiji Gakuin University, and apprenticed with photographer Masato Terauchi. He contributed to the first issue of photography magazine PHaT PHOTO and became an independent photographer after that, in 2003. The author of many books, Kohno not only shoots all sorts of commercial photographs, but also writes prolifically for camera and other magazines.