Shutter speed: freeze motion or let it blur

Lesson 2 of 8

Shutter speed is how long the sensor collects light. It controls how bright the photo is, but it also decides how movement looks, and that often matters more.

The idea

Shutter speeds are written as fractions of a second: 1/1000 is a thousandth of a second, 1/30 is a thirtieth. Anything that moves while the shutter is open leaves a smear across the photo. A short shutter catches a moment and freezes it. A long shutter records the whole movement as blur.

Neither is wrong. A sharp splash of water and a silky waterfall are both good photos. What matters is choosing.

Rough starting points. Faster subjects, and subjects closer to you, need faster speeds.

Two kinds of blur

Subject blur: the thing you photographed moved. Only a faster shutter fixes it.
Camera shake: your hands moved. Everything is smeared, even things that were standing still. The iPhone's stabilisation helps a lot here, and so does bracing your elbows against your body or leaning on a wall.

Stabilisation steadies the phone, not the scene. A slow shutter can keep a building sharp while a person walking past is still a blur.

Every shutter change is an exposure change

A faster shutter lets in less light, so something else has to make up for it. On an iPhone that's ISO. Go from 1/125 to 1/500 (two stops faster) and the ISO has to go up two stops to keep the same brightness. In bright daylight that's no problem. Indoors or at dusk it can push ISO high enough to show noise, which is the next lesson.

In Chobial

Open the controls and tap MODE, then S (shutter priority). You choose the shutter speed; Chobial chooses the ISO to match.
Tap SHUTTER. Its dial opens on the right. Drag up for more (slower, more light) and down for less.
Tap AUTO on the dial to give the shutter back to the camera.

Even in P, Chobial thinks about motion. When it's following a person, it keeps the shutter at 1/60 s or faster; for a pet, 1/125 s or faster. Tap inside the white corners around a person or pet to follow them. They turn green.

For moments that don't wait, hold the shutter button for a burst. Chobial keeps shooting as fast as the camera is ready, and you pick the best frame afterwards.

Freeze it, then blur it

Find something that moves steadily: a tap running, a fan, traffic, a friend walking past.
Switch to S and set the shutter to 1/1000. Take a photo.
Set 1/60 and take another, then 1/8 with the phone propped against something solid.
Compare the three in the Library. Notice how the ISO in ⓘ fell as the shutter slowed.

Slow shutters need a steady phone. Chobial's shutter goes down to about a second, depending on the phone. Rest the phone on a wall or a bag, or use a small tripod. With an Apple Watch you can fire it from your wrist with a 3 or 10 second timer, so your finger doesn't shake it.

Next: what happens to the other half of the balance, in ISO and noise.

Questions

What's the slowest shutter speed I can hold by hand?

iPhones have very good stabilisation, so for a still subject around 1/15 to 1/30 s is often sharp if you hold your breath and brace your arms. Moving people need faster speeds whatever the stabilisation does, because it steadies the phone, not them.

Why is my photo blurry even though the shutter was fast?

Probably focus, not motion. If only one part is soft and the rest is sharp, the camera focused on the wrong thing. See the lesson on focus.

Why does my photo get grainy when I pick a fast shutter indoors?

In S mode the camera raises ISO to make up for the light a fast shutter throws away. Indoors that can mean a high ISO and visible noise. Choose the slowest shutter that still freezes your subject.