Apple Aperture Digital Photography Fundamentals - Manual (Page 16)

16 Chapter 1 How Digital Cameras Capture Images
Telephoto lenses (with long focal lengths) tend to have shallow focus when the
aperture is opened all the way, limiting the depth of field of an image. Wide-angle
lenses (with short focal lengths) tend to create images with great depth of field
regardless of the aperture setting.
Shutter
The shutter is a complicated mechanism that precisely controls the duration of time
that light passing through the lens remains in contact with the digital image sensor.
The camera’s shutter is activated by the shutter release button.
Prior to the digital age, the shutter remained closed to prevent the film from being
exposed. Depending on the type of digital image sensor, a mechanical shutter may not
be necessary. Rather than a shutter revealing light to initiate a chemical reaction in the
film, the digital image sensor may simply be turned on and off.
Shallow depth of field
Only the foreground is in focus. Great depth of field
The image is in focus from the
foreground to the background.