Camera and f-number
Intermediate
Aperture controls exposure and depth of field.
The f-number N = f/D controls how much light enters; each stop (f/2.8, 4, 5.6...) halves the light. Smaller aperture increases depth of field.
f/2 lets in 4 times as much light as f/4.
Exposure is a trade-off with shutter time.
In more detail
A camera forms a real, inverted image on a sensor through a lens. The f-number, N = f/D, sets the aperture size and controls brightness and depth of field.
Real-world uses
- Photographers choose f-numbers to control depth of field.
- Smartphone cameras use small apertures for wide depth of field.
- Photographers choose the f-number to control how much light reaches the sensor and how blurred the background looks.
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Frequently asked questions
Does a lower f-number let in more light?
Yes, because the aperture is larger for a given focal length.
What is depth of field?
The range of distances that appear sharp in a photo.
What does a higher f-number mean?
A smaller aperture, which lets in less light but gives a greater depth of field.
Related topics in Optics
Compound microscope · Astronomical telescope · Reflecting telescope · Wave theory of light · Huygens' principle · Coherent sources