Start with the stop
A “stop” is a doubling or halving of light. All three settings are measured in stops, which is why they can be traded: open the aperture one stop, use a shutter speed one stop faster, and the brightness stays the same.
Aperture: how much light
Aperture is written as an f-number, such as f/2.8 or f/8. The f-number is the lens’s focal length divided by the diameter of its opening, so a smaller number means a wider opening and a brighter photo.
f/1.4 · f/2 · f/2.8 · f/4 · f/5.6 · f/8 · f/11 · f/16
Each step to the right is one stop darker and lets in half the light.
The side effect is depth of field. A wide aperture (small f-number) blurs everything in front of and behind the focus point, which is why it’s used for portraits. A narrow aperture (large f-number) keeps near and far sharp, which suits landscapes.
Shutter speed: for how long
Shutter speed is how long the sensor collects light, usually written in fractions of a second.
1/1000 · 1/500 · 1/250 · 1/125 · 1/60 · 1/30 · 1/15
Each step to the right is one stop brighter: the light is collected for twice as long.
The side effect is motion blur. A fast shutter freezes a runner or a splash; a slow one lets moving things smear and makes camera shake more likely. A common rule of thumb for handheld shots: don’t go slower than one over the (35mm-equivalent) focal length, so 1/50 s or faster at 50mm. With image stabilization you can go slower.
ISO: how much amplification
The higher the ISO, the brighter the same light turns out.
ISO 100 · 200 · 400 · 800 · 1600 · 3200
Each step to the right is one stop brighter.
The side effect is noise. High ISO brings speckles of colour and softer detail. When there’s enough light, keep ISO low.
Three settings, same brightness
| Aperture | Shutter | ISO | What changes |
|---|---|---|---|
| f/2.8 | 1/500 | 100 | Strong background blur, motion frozen |
| f/4 | 1/250 | 100 | Aperture one stop narrower, shutter one stop slower to compensate |
| f/4 | 1/500 | 200 | Shutter one stop faster, ISO one stop higher; slightly more noise |
All three rows give the same brightness. They differ in depth of field, motion and image quality, so pick the one that matters most for the shot.
The sunny 16 rule
An old method for when you have no light meter: in bright, direct sun, set f/16 and a shutter speed of one over the ISO. At ISO 100 that’s 1/100 s, or 1/125 on most cameras. In overcast light or open shade, open up one or two stops.
The numbers on film boxes
A roll of film has one fixed sensitivity: every frame on a 400-speed roll is ISO 400, which is why film boxes print that number so large. FilmTable’s boxes follow the same habit: the numbers in PTR 400, GLD 200 and VLV 50 are film speeds, and the T in NEON 800T is the traditional mark for tungsten-balanced film made for indoor light. In the app they’re just filter names; they don’t change the photo’s exposure.
What you can change on an iPhone
- Aperture: most iPhone lenses have a fixed aperture. The Camera app balances shutter speed and ISO for you, raising ISO or switching to Night mode for longer exposures when it’s dark.
- Exposure compensation: what you control directly is overall brightness. Tap to focus, then drag the sun icon beside the focus box up or down.
- Shutter speed and ISO: to set these yourself, use a third-party camera app with manual controls.
All three values are saved in the photo’s EXIF data; see how to read EXIF data. If a photo came out too bright, see how to fix overexposed photos.