A wide aperture and a narrow aperture can produce two very different photographs of the same subject. This lesson compares them directly so that you can choose on purpose instead of leaving it to the camera.
Definitions
- Wide: f/1.4 to f/2.8. A large opening, low f-number.
- Middle: f/4 to f/8.
- Narrow: f/11 to f/22. A small opening, high f-number.
Comparison
| Wide (f/1.4–f/2.8) | Narrow (f/11–f/22) | |
|---|---|---|
| Light admitted | A lot | Little |
| Depth of field | Shallow; background blurred | Deep; near and far both sharp |
| Shutter speed in the same light | Fast | Slow |
| Focusing accuracy needed | High; small errors show | Low; errors are hidden |
| Lens sharpness | Slightly soft at the edges, some dark corners | Softened overall by diffraction beyond f/16 |
| Points of light | Render as soft discs when out of focus | Render as starbursts |
| Sensor dust | Invisible | Shows as dark spots in skies |
What a wide aperture is good for
A wide aperture isolates. With the background reduced to a soft wash of colour, attention goes to the subject. This is the standard approach for portraits, details at weddings, food and any situation with a cluttered background that cannot be changed. The quality of the out-of-focus area is known as bokeh.
It is also the practical choice in low light. At f/1.8 a lens gathers about ten times as much light as at f/5.6, which is the difference between ISO 6400 and ISO 640 in the same room.
Typical settings: a head-and-shoulders portrait in shade at f/2, 1/500 s, ISO 100. A candlelit dinner table at f/1.8, 1/60 s, ISO 3200.
What a narrow aperture is good for
A narrow aperture includes. It keeps the whole scene sharp, which suits landscapes, architecture, interiors and group photos arranged in several rows. It is also used to force a slow shutter speed in daylight for effects such as smooth flowing water.
Typical settings: a landscape on a tripod at f/11, 1/30 s, ISO 100. A waterfall under cloud at f/16, 1 s, ISO 100. A city at night with starburst street lamps at f/11, 10 s, ISO 100.
The middle range
Apertures from f/4 to f/8 are easy to overlook, yet they are where most lenses are sharpest and where focusing is forgiving. For travel, street and documentary photography, f/5.6 or f/8 is a dependable default. When unsure, start at f/5.6.
Depth of field depends on distance too
The same f-number gives very different results at different distances. At f/2.8, a face photographed from one metre has only a few centimetres in focus, while a building photographed from fifty metres is sharp throughout. To increase background blur without changing the aperture, move closer to the subject, use a longer focal length and increase the distance between subject and background.
Common mistakes
- Using the widest aperture for every portrait. At f/1.4 from close range, one eye may be sharp and the other soft. Focus on the nearer eye, or stop down to f/2.8.
- Photographing a group wide open. Use f/5.6 or f/8 for two or more rows.
- Choosing f/22 for landscapes “for maximum sharpness”. The depth of field increases, but diffraction lowers overall sharpness. f/8 to f/11 is usually better.
- Stopping down indoors without noticing that the shutter speed has dropped to 1/8 s.
- Using a wide aperture in bright sun and overexposing because the camera has reached its fastest shutter speed. Lower the ISO to base or stop down.
Practice exercise
- Line up three small objects in a row leading away from the camera, about 30 cm apart, with the nearest one about a metre away.
- In Aperture Priority, focus on the middle object and shoot at the widest aperture.
- Repeat at f/5.6 and at f/16, always focusing on the middle object.
- Find the aperture at which all three first appear sharp.
- Repeat the series from twice the distance and see how the result changes.
Next in this series: What Is Aperture in Photography?, What Is an f-Stop? and How to Balance ISO, Aperture and Shutter Speed. You can also browse all photography lessons.
