Aperture is the adjustable opening inside a lens. It controls how much light passes through the lens, but it also affects how much of the scene appears acceptably sharp from front to back.
Why does a smaller f-number mean a larger opening?
The f-number is a ratio. That is why f/2.8 is a larger opening than f/8 even though 2.8 is the smaller number.
What changes when you open the aperture?
- More light reaches the sensor.
- You can often use a faster shutter speed or lower ISO.
- Depth of field usually becomes shallower.
- Background blur can become stronger when subject distance and focal length also support it.
What changes when you stop the aperture down?
- Less light reaches the sensor.
- Depth of field usually becomes deeper.
- You may need a slower shutter speed, higher ISO, or more light.
Is f/2.8 always blurry in the background?
No. Aperture is only one part of depth of field. Focal length, subject distance, background distance, and sensor size also affect the result.
What does a constant f/2.8 zoom mean?
A zoom such as a 24-70mm f/2.8 or 70-200mm f/2.8 can keep f/2.8 available throughout the zoom range. A variable-aperture zoom might be labeled 18-45mm f/4.5-6.3, meaning the widest available aperture becomes smaller as you zoom in.
Why does aperture matter when buying a lens?
A wider maximum aperture can help in low light and make shallow depth of field easier to achieve, but it usually adds size, weight, complexity, and cost. A slower lens may be completely adequate for daylight, travel, landscapes, or situations where you want deeper focus anyway.