Canon EOS 3 User Manual (en)

2. Aperture-Priority AE (Av): 
You Set the Aperture
In this mode, you set the desired aperture and the camera sets the
shutter speed automatically to suit the subject brightness.
The larger the aperture (smaller F-number like f/1.4) the more blurred the
background will be. This effect is suited for portraits. The smaller the
aperture (larger F-number like f/22), the clearer the focus will be for both
near and far objects. 
With a large aperture
With a small aperture
While pressing the <
button, turn the <
> dial until Av
appears on the LCD panel.
Av is an abbreviation for Aperture value.
 06. C836-E (61~)  28-01-2003  11:48  Pagina 65