ISO and noise: shooting when the light runs out

Lesson 3 of 8

When there isn't enough light for the shutter speed you need, ISO is how the camera makes up the difference. It's how you get a photo at all in a dim room, but it comes at a price: noise.

The idea

ISO is amplification. The sensor collects a certain amount of light, and ISO sets how much that signal is boosted before it becomes a photo. ISO 100 is a little boost; ISO 1600 is sixteen times more, four stops brighter from exactly the same light.

The catch is that amplification doesn't add light. It makes everything louder, including the random flicker every sensor produces. In a bright scene that flicker is tiny next to the real signal. In a dark one it isn't, and it shows up as speckles, blotches of colour and mushy detail, mostly in the shadows. That's noise.

So the rule is simple: use the lowest ISO you can get away with, and raise it only when the shutter speed would otherwise be too slow.

A dark photo or a noisy one?

At dusk you'll hit a choice. Keep ISO low and the shutter slows until the photo blurs. Raise ISO and the photo stays sharp, with some noise. A sharp, slightly noisy photo is almost always better than a clean blurry one. Noise can be reduced afterwards, or look like film grain. Blur can't be undone.

Why the Camera app looks cleaner at night. Apple's Camera app hides noise by merging many frames into one and smoothing what's left. A RAW from Chobial keeps much more of what the sensor actually saw. That means more real detail and more tonal range to work with, and more visible noise in deep shadow too.

In Chobial

Open the controls, tap MODE and choose ISO (ISO priority). You choose the ISO; Chobial chooses the shutter speed.
Tap ISO. Its dial opens on the right. Each step is a stop. The range depends on the lens you're using.
Watch the shutter speed in the readout. If it drops below about 1/30, hold very still or raise ISO.

In S mode it works the other way round: you set the shutter, and Chobial raises ISO as far as it needs to. In P, Chobial balances the two for you.

After the shot, Chobial's films can help. Every film has a Develop section with noise reduction and sharpening for the negative, and an Effects section with grain modelled on real film stocks. A little film grain over a noisy photo often looks better than trying to smooth it all away. For more, read why digital grain looks fake.

Find your phone's noise limit

In a dim room, set up something with dark areas and fine texture: a bookshelf, a jumper, a plant.
Switch to ISO mode. Take a photo at the lowest ISO, holding very still or resting the phone on something.
Take more photos, raising ISO a couple of steps each time, until you reach the top of the dial.
In the Library, pinch to zoom into the shadows of each. Find the highest ISO you'd still be happy with. That's your personal limit for this lens.
Try the same on the 0.5× or 2× lens from the lens pill. Smaller sensors get noisy sooner.

The main lens is the best in low light. On most iPhones the 1× lens has the largest sensor and the widest aperture. When light is short, use it and step closer rather than zooming.

You've now got both controls. Next, the tool that tells you whether you've used them well: the histogram.

Questions

What ISO should I use?

The lowest one that still gives you a fast enough shutter for your subject. In daylight that's usually the phone's lowest ISO. Indoors and at night, accept a higher ISO rather than a blurry photo.

Is noise the same as grain?

No, though they're related. Noise is random speckle from the sensor, strongest in the shadows and often coloured. Film grain has its own structure and follows the tones of the photo. Chobial's films add grain modelled on real stocks, which can make a noisy photo look intentional.

Why is the ISO range different when I switch lenses?

Each iPhone lens has its own sensor, and each has its own range of ISO. Chobial's dial shows only what the lens you're using can do.