Open and Close the Iris

Drag the ring. Watch light and depth of field trade off.

f/2.8
f/1.4 f/2 f/2.8 f/4 f/5.6 f/8 f/16
Shallow depth of field
Light
More
DOF
Shallow
The trade-off

Open one stop: double the light, half the sharp zone. Stop down: the reverse.

Reading F-Stops

The number is a fraction, which is why it runs backwards

F-number = focal length ÷ opening width. The opening is the denominator, so a bigger hole = smaller number: f/1.8 is wide, f/16 is narrow. Each step below halves the light.

Aperture
  1. f/1.4
  2. f/2
  3. f/2.8
  4. f/4
  5. f/5.6
  6. f/8
  7. f/11
  8. f/16
  9. f/22
more light · less depthless light · more depth

Light

exposure

Wider = more light = faster shutter or lower ISO. Fast f/1.4–f/1.8 lenses suit indoor and low-light work.

Depth of Field

focus zone

Wide = thin slice sharp, rest blurred. Narrow = front-to-back in focus.

Sharpness

diffraction

Peak at f/5.6–f/8. Wide open is soft; past f/11–f/16 diffraction softens the whole frame.

Which F-Stop, When

Start here, then fine-tune for your scene

f/1.2–2.8

Subject isolation

Portraits, products, low light. Maximum blur and light; the focus plane is very shallow, so lock on the nearest eye.

f/1.8 headshots f/2.8 events
f/4–5.6

Everyday & groups

Environmental portraits, small groups, street. Faces stay sharp while the background still separates.

f/4 couples f/5.6 street
f/8

Maximum detail

The sharpness sweet spot. Groups, documentation, and any time the cleanest image matters most.

f/8 groups f/8 repro
f/11–16

Deep focus

Landscapes and architecture, foreground to horizon sharp. f/16 renders sunstars from point lights.

f/11 landscape f/16 sunstars

Setting Aperture in the Field

Four steps, in order

  1. Blur or sharp?

    Background falls away → wide. Stays sharp → narrow. Decide first.

  2. Aperture Priority

    You set the f-stop; the camera sets shutter.

    A / Av Auto ISO
  3. Watch the shutter

    Stopping down slows it. Below 1/focal length, raise ISO or open back up.

  4. Lock focus wide open

    At f/1.4–f/2 the sharp zone is a few centimeters. Use single-point AF on the eye; if focus misses, stop down to f/2.8.

Cheat Sheet

Quick answers for the field

Blurry background? Open to f/1.8–f/2.8, step back, zoom in
Everything sharp? f/8–f/11 and focus a third into the scene
Group photo? f/5.6 or smaller so every face is sharp
Sharpest result? Two stops from wide open (~f/5.6–f/8)
Low light? Widest aperture first, then raise ISO
Want sunstars? f/16 against a point light source
Soft at f/22? Diffraction softens it; drop to f/11
Portrait missing focus? Single-point AF on the eye, or stop to f/2.8

Common Questions

Quick answers on f-stops, depth of field, and lens sharpness.

What is aperture?

The opening in your lens, set by the f-number. Wider = more light and blur; narrower = less light, more sharp.

Why is a lower f-number a bigger opening?

It's focal length ÷ opening width. The opening is the denominator, so a bigger hole gives a smaller number: f/1.8 wide, f/16 narrow.

What is the sharpest aperture?

Two to three stops from wide open, usually f/5.6–f/8. Wider is soft; past f/11–f/16 diffraction softens everything.

Does aperture affect shutter speed?

Yes. Open one stop → shutter one stop faster (or ISO one stop lower) for the same brightness. That's the exposure triangle.

Keep Learning

The settings that balance against aperture