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Aperture-Priority AE Technique #1: The Relationship Between Lens Aperture and Bokeh

Photos with bokeh effects are the signature of a DSLR camera with a large sensor. The magnitude of the bokeh effect can be controlled by opening and closing the lens aperture. One special characteristic of bokeh lies in how the main subject appears to rise to the fore when the bokeh effect is magnified, imparting a soft impression to the picture. (Reported by: Teppei Kohno)


Use aperture to control the bokeh effect

To take a picture with a soft background bokeh effect, it is necessary to control the aperture. Aperture refers to the hole that allows light to enter the camera. The larger this hole is opened, the narrower the focus range (depth of field) gets, leading to a larger bokeh effect. Aperture is expressed by a figure known as the f-number—the smaller the number, the larger the hole (aperture) and the larger the bokeh effect.

For more about the relationship between aperture value and aperture opening, click here.

Normally, the f-number cannot be fixed as desired in [P]mode. When shooting flowers, for example, while a beautiful picture can be taken in this mode, it is difficult to defocus the background to make the main subject stand out. This is when the Aperture-priority mode can be used, as the f-number can be adjusted and fixed to a desired value in this mode. This is therefore a mode that allows you to control the extent of the bokeh effect to match your photographic intent.

OK f/2.8

The main subject stands out with a lovely bokeh effect in the background.


NG f/8

If the focus is on the entire scene, the picture becomes a descriptive photograph.


Checking a lens' available aperture values

The maximum aperture, which indicates the brightness of the lens, varies according to the lens used. The maximum aperture is also stated in the name of the lens. In a zoom lens, the maximum aperture may vary at the wide-angle and telephoto ends. In this case, 2 f-numbers are stated, with the first being the maximum aperture at the wide angle end and the second, the maximum aperture at the telephoto end.

The name of an EF lens will always contain a numerical portion starting with “f”. This portion expresses the lens' maximum aperture.

For the EF-S18-55mm f/3.5-5.6 IS STM which is often adopted in kit lenses, the name of the lens is stated on the periphery of the lens surface. This means that the lens has a maximum aperture of f/3.5 at the wide angle end and f/5.6 at the telephoto end.



Use the “Portrait” Picture Style for shooting flowers

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.

Photo taken with the "Standard" Picture Style. The picture looks fairly vivid and lively but there is still something lacking.


Photo taken with the "Portrait" Picture Style.
The colours and vividness are emphasised more strongly in this depiction.


How to use the Aperture-priority mode For EOS 700D

1. Set the camera to [Av] mode.

Turn [ON] the power supply and adjust the Mode Dial to the [Av] mode.


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 is changed.

The current f-number will appear on the rear LCD screen in the area circled out on the above image. Turn the Main Dial and check that the f-number has changed before taking the picture.



Teppei Kohno

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.