Aperture is the opening inside a lens that lets light reach the sensor, described with f-numbers such as f/1.8 or f/8. A small f-number means a large opening, more light and a shallower zone of sharpness. A large f-number means a small opening, less light and more of the scene in focus.
Understanding F-Numbers
The f-number is the focal length divided by the opening diameter, which is why the scale feels backward at first. The usual full-stop sequence runs f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16. Each step lets in half as much light as the one before. Many cameras also allow intermediate settings in thirds of a stop.
Depth of Field
Depth of field is the range of distance that looks acceptably sharp. Three things control it: aperture, focal length and the distance to your subject. Wider apertures, longer lenses and closer subjects all make the zone thinner and the background softer.
- Portraits: wide apertures such as f/2 isolate the subject.
- Landscapes: f/8 to f/11 keeps near and far both sharp.
- Group photos: a mid aperture makes sure that everyone is in focus.
- Macro: even small apertures give thin focus zones, so plan carefully.
The Sharpest Setting
Lenses are often at their best a stop or two down from wide open. Very small apertures like f/22 can cause diffraction, a softening effect from light bending around the blades. Check a lens’s behaviour on your own images instead of relying on a general rule.
Quick Reference
| Aperture | Light | Typical result |
|---|---|---|
| f/1.4 to f/2.8 | Plenty | Thin focus, soft background |
| f/4 to f/5.6 | Moderate | Balanced, flexible |
| f/8 to f/11 | Less | Deep focus, crisp results |
| f/16 and beyond | Little | Very deep focus, risk of diffraction |
Try This
- Set aperture priority mode, shown as A or Av.
- Place an object a short distance away with a busy background.
- Photograph it at your widest aperture, then at f/5.6, then at f/11.
- Compare how the background changes and how the shutter speed adjusts.
- Repeat with the object further from the camera and note the difference.
Aperture and the Look of Blur
The quality of blur, often called bokeh, depends on more than the f-number. The shape of the aperture blades, the lens design and the distance to the background all change how highlights appear. Rounded blades tend to give smooth circles, while straighter edges can create polygon shapes. Looking at sample photos from a lens shows more than a number can.
FAQ
Why do some lenses have a changing maximum aperture?
On many zooms, the widest opening gets smaller as you zoom in, such as f/3.5 at the wide end and f/5.6 at the long end. Constant-aperture zooms keep the same value but are usually larger.
Does aperture change exposure only?
No. It also changes depth of field, and it can influence sharpness and the look of out-of-focus areas.
The Short Version
Aperture controls light and depth of field. Use wide openings for blur and low light, and narrower ones for deep focus. Learn how your own lenses behave at different settings.
