The aperture is an adjustable opening in the lens that controls the amount of light and depth of field in the image. A small f-number means a large opening with a lot of light and shallow depth of field (ideal for portraits), while a large f-number means a small opening with little light and a large depth of field (ideal for landscapes). The aperture is a central parameter for image composition.
Category: Photography Basics > 3. Exposure & Camera Settings Article ID: 3.2 Created: May 2026
The Key Points in Brief
- The aperture is an adjustable opening in the lens – it controls how much light falls on the sensor per unit of time
- It is indicated as the f-number (e.g., f/2.8 or f/8) – small number = wide open = lots of light; large number = narrowly closed = little light
- The aperture has two effects: it influences brightness and depth of field
Explanation
What is the aperture?
The aperture is an adjustable opening made up of several blades inside the lens. Depending on the setting, it lets more or less light onto the sensor – similar to the pupil of the eye, which dilates in darkness and contracts in bright light.
Important: The term “aperture” is commonly used for two things:
- The component itself (the blade mechanism inside the lens)
- The aperture value (the setting, i.e., the f-number)
The f-number – and why it works inversely
The aperture value (f-number) is the ratio of focal length to the effective diameter of the aperture opening:
f-number = focal length ÷ aperture diameter
This leads to a logic that often confuses beginners at first:
- Small f-number (e.g., f/1.4 or f/2.8) → aperture wide open → lots of light → bright image
- Large f-number (e.g., f/11 or f/16) → aperture narrowly closed → little light → darker image
Memory aid: A small f-number = a “small” (low) number, but a large opening. Think of it like a fraction: f/2 is larger than f/16, just like ½ is larger than 1/16.
Standardized aperture stops
The most common full aperture stops are:
f/1 – f/1.4 – f/2 – f/2.8 – f/4 – f/5.6 – f/8 – f/11 – f/16 – f/22
Each step halves or doubles the amount of incoming light:
- Closing one stop (e.g., f/2.8 → f/4): half as much light → shutter speed must be doubled
- Opening one stop (e.g., f/8 → f/5.6): twice as much light → shutter speed can be halved
Many cameras also offer half or third stops for finer control.
The aperture’s second effect: depth of field
Besides brightness, the aperture crucially influences how much of the image appears sharp – the so-called depth of field:
- Wide aperture (small f-number, e.g., f/1.8) → shallow depth of field → only the main subject is sharp, the background blurs (bokeh effect) → ideal for portraits
- Narrow aperture (large f-number, e.g., f/11) → large depth of field → foreground and background are sharp simultaneously → ideal for landscape photos
Aperture values and their typical uses
| Aperture Range | Depth of Field | Typical Use |
|---|---|---|
| f/1.4 – f/2.8 | Very shallow | Portraits, night shots, isolating subjects |
| f/4 – f/5.6 | Medium | All-round, travel photography |
| f/8 – f/11 | Large | Landscape, architecture, group photos |
| f/16 – f/22 | Very large | Macro, maximum depth of field |
Lens brightness
The brightness of a lens describes the smallest achievable f-number (maximum opening). A lens with f/1.4 is “brighter” than one with f/4 – it lets in four times more light at the same exposure time. Bright lenses are more expensive but indispensable for low light and creative depth of field control.
Practical Tip
The aperture is the most powerful creative parameter of the three exposure variables. A simple way to start: try the aperture priority mode (A or Av) – you choose the aperture, and the camera automatically adjusts the shutter speed. Start with f/1.8 for an isolated subject and f/11 for a landscape – the difference in image effect will be immediately visible.