Aperture settings control how much light reaches the sensor and how much of the scene appears acceptably sharp. They do not normally change the composition or framing. Aperture stops describe predictable exposure changes, while camera field of view is set mainly by focal length and sensor size.
To change framing, use a different focal length, move the camera, change the sensor format, or crop the image. To change brightness and depth of field without changing the lens’s framing, change the aperture.
How Aperture Settings Are Numbered: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, and f/32
An f-number expresses the lens’s focal length divided by the diameter of its entrance pupil. A lower number means a larger opening: f/2 admits more light than f/8. A higher number means a smaller opening and less light.
The common full-stop sequence is:
- f/1, f/1.4, f/2, f/2.8, f/4, f/5.6
- f/8, f/11, f/16, f/22, f/32
Each step changes the opening diameter by approximately 1.4 times, but the opening’s area changes by a factor of two. Modern cameras usually offer half-stop or third-stop increments between these full stops, such as f/4.5 or f/6.3.
What Aperture Stops Change: One Stop Doubles or Halves Light
Opening the aperture by one full stop doubles the light reaching the sensor. For example, changing from f/8 to f/5.6 gives twice as much light. Closing it from f/8 to f/11 halves the light. These changes assume the shutter speed and ISO remain constant, so the recorded image becomes one stop brighter or darker.
To keep the same exposure, compensate with another control:
- Change f/8 to f/5.6, then use a shutter speed twice as fast, such as 1/125 to 1/250 second.
- Change f/8 to f/11, then use a shutter speed twice as slow, such as 1/125 to 1/60 second.
- Adjust ISO by one stop in the opposite direction when shutter speed must remain fixed.
Aperture also changes depth of field. A wider setting such as f/2.8 produces a narrower zone of acceptable sharpness, useful for isolating a subject. A narrower setting such as f/11 produces more depth of field, provided the exposure is adjusted. Depth of field also depends on focal length, subject distance, sensor format, and the viewing size of the final image.
What Camera Field of View Means: Focal Length and Sensor Size Set Framing
Camera field of view is the angular portion of the scene recorded by the image. It can be described horizontally, vertically, or diagonally. A wider field of view includes more of the surroundings; a narrower field of view shows a smaller area with greater apparent magnification.
Focal length and sensor size determine this angle. On the same sensor, a 24mm lens captures a wider view than a 50mm lens from the same camera position. With the same lens, a smaller sensor captures a narrower portion of the image circle than a larger sensor. For example, assuming a common 1.5x crop factor, a 35mm lens on an APS-C camera gives a similar framing to a 50mm lens on a full-frame camera.
These comparisons require the camera position and subject distance to stay the same. Moving closer or farther changes the framing and the perspective relationships between objects, even if the focal length does not change.
Aperture Versus Framing Controls: Same Position, Same Framing, Different Depth of Field
Imagine a camera fixed on a tripod, focused on a subject three metres away, with a 50mm lens. At f/2.8, f/4, f/5.6, and f/8, the field of view remains essentially the same when focus and camera position are unchanged. The subject occupies the same part of the frame, but each full-stop change alters exposure and depth of field.
Changing from f/2.8 to f/8 closes the aperture by three stops: f/4 is one stop, f/5.6 is two, and f/8 is three. That reduces light by eight times. To preserve the exposure, change 1/125 second to 1/15 second, or raise ISO 100 to ISO 800. The slower shutter speed may require a tripod or a static subject.
For a wider composition, change the 50mm lens to a shorter focal length or move the camera backward. Moving changes perspective; changing focal length changes the angle of view. Changing sensor size or cropping also changes how much of the scene appears in the final frame. Aperture changes brightness and focus depth, not the lens’s geometric field of view.