What Is Aperture (f-number) in Cameras and Phones?
Aperture, or the f-number, decides how much light a lens lets in and how strongly the background blurs. Here is what f/1.8 means and which number to choose.
What is aperture?
Aperture is the adjustable opening inside a lens that lets light reach the sensor. Its size is written as an f-number: f/1.8, f/2.8, f/5.6 and so on. One rule matters most: the smaller the number, the wider the opening and the more light the lens lets in. f/1.8 is a wide opening; f/16 is a tiny pinhole.
The two things aperture controls
How much light. A wide aperture (f/1.8, f/2.0) gathers plenty of light, so you can shoot at dusk without a flash and without blurry frames. In a dark restaurant or at a party, a bright lens is the single biggest advantage.
Depth of field (the background). A wide aperture keeps only a thin slice sharp and blurs the background beautifully — an effect called bokeh. That is why portraits at f/1.8 look professional: the face is sharp, the background softly blurred. A narrow aperture (f/8, f/11) keeps everything sharp, which suits landscapes.
The f-number scale
Each full stop halves or doubles the amount of light:
| f-number | Opening | Light |
|---|---|---|
| f/1.4 | very wide | most |
| f/2.8 | wide | a lot |
| f/5.6 | medium | medium |
| f/11 | narrow | little |
What to look for when buying
On cameras with interchangeable lenses, the lens sets the aperture, not the camera body. Cheap kit lenses often have a variable aperture (e.g. f/3.5–5.6) — they let in less light as you zoom. Bright prime lenses (f/1.8) cost more but deliver the best results in low light and for portraits.
Compact cameras such as the Sony ZV-1 come with a bright f/1.8–2.8 lens — one reason it is a favourite among vloggers. If you want full freedom to choose lenses, the Canon EOS R8 or Fujifilm X-T5 are strong picks.
Phones cannot change aperture — it is fixed. Even so, the numbers matter: the main camera on the Xiaomi 15 is f/1.62, and the Samsung Galaxy S25 Ultra is f/1.7. The lower the number, the better the phone shoots in the dark.
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