Quick answer: Aperture is the adjustable opening inside your lens that lets light through. It’s measured in f-stops such as f/1.8, f/4 or f/11. A smaller f-number means a bigger opening: more light and a blurrier background. A bigger f-number means a smaller opening: less light and more of the scene in focus.
Why Small Numbers Mean Big Openings
The f-number is a ratio: focal length divided by the diameter of the opening. On a 50mm lens, f/2 means a 25mm opening and f/8 means about a 6mm opening. Each full stop (f/2.8 → f/4 → f/5.6 → f/8) cuts the light in half.
Aperture Cheat Sheet
| Aperture | Depth of field | Best for |
|---|---|---|
| f/1.2 – f/2 | Very shallow | Portraits, low light, creamy background blur |
| f/2.8 – f/4 | Shallow to moderate | Events, pets, food, indoor sports |
| f/5.6 – f/8 | Moderate to deep | Street, travel, groups, sharpest results on many lenses |
| f/11 – f/16 | Deep | Landscapes, architecture, sunstars |
| f/22 and smaller | Very deep but softer | Long exposures; diffraction reduces sharpness |
Aperture and the Exposure Triangle
Aperture works with shutter speed and ISO. Open the aperture by one stop and you can use a shutter speed twice as fast for the same brightness. That’s why “fast” lenses (f/1.8 or f/1.4) are prized for low light and action indoors.
Depth of Field Depends on More Than Aperture
- Distance: the closer you are to your subject, the shallower the focus.
- Focal length: longer lenses make backgrounds look blurrier.
- Sensor size: full-frame cameras give shallower depth of field at the same framing; see full frame vs crop sensor.
How to Control Aperture
- Choose Aperture Priority (A on Nikon/Sony, Av on Canon).
- Turn the dial to pick the f-number; the camera sets the shutter speed.
- Raise ISO if the shutter speed drops too low to hold steady.
- Some older lenses use an aperture ring; see what A and M mean on Nikon lenses for related switches.
Common Mistakes
- Shooting group photos at f/1.8, leaving people at the back blurry. Use f/4–f/5.6.
- Stopping down to f/22 for landscapes. f/8–f/11 is usually sharper.
- Forgetting that phones simulate blur with software rather than a real aperture. Compare in point-and-shoot vs iPhone.
Frequently Asked Questions
What is the best aperture for portraits?
f/1.8 to f/2.8 for one person; f/4 or more for couples and groups.
Is f/1.8 better than f/4?
It gathers four times more light and blurs backgrounds more, but the lens is often bigger and pricier.
Does aperture change the zoom?
No. Aperture changes light and focus depth, not magnification.
