Aperture and depth of field

In short: The aperture is an opening in the lens that determines how much light reaches the sensor. A large aperture (small number such as f/1.8) gives a lot of light and shallow depth of field, a small aperture (f/11) great depth of field.

In more detail: The f-number is the ratio of focal length to opening diameter. Each full stop halves or doubles the amount of light.

In detail

• F-stop series: f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22. The higher, the less light.
• Depth of field: The range that appears sharp in the picture. A large aperture blurs the background (bokeh), suited to portraits.
• Landscape: Smaller aperture (f/8–f/11) for sharpness throughout.
• Diffraction: At very small apertures (f/22) sharpness suffers.
• Sweet spot: Many lenses are sharpest at f/5.6–f/8.
• Interplay: Aperture, shutter speed and ISO form the exposure triangle (fotografie-grundlagen-belichtungsdreieck-raw-und-jpeg, verschlusszeit-und-bewegung).