Camera sensitivity is a very dense subject, with so many factors to consider it’s hard not to make an entire series of Practicals about each one. So for convenience sake, this episode of Practicals covers the broad strokes of camera sensitivity, or ISO.
Your ISO, along with shutter speed and aperture, is one of the three main factors you adjust to get a proper exposure.
ISO is an industry standard that manufacturers follow to measure a camera sensor’s sensitivity. Every camera has a different range of ISO levels it can operate at. On any camera though, a low ISO means your sensor will be less reactive to light, while a high ISO means it will be more reactive. Every time you double your ISO, your sensor requires half as much light to get a proper exposure. So higher ISO levels are normally used at night or in interiors where it is dark. Lower levels are used when light is plentiful, such as during a sunny day.
Base vs Native ISO
Two terms you will hear when talking camera sensitivity is “Base ISO” and “Native ISO”. Base ISOrefers to the lowest ISO level your camera can operate at while still getting a good exposure.
Native ISOrefers to the ISO level your camera operates best at. At your native ISO,all the pixels on your camera’s sensor are reading light, but the image is still clean, with “noise” at a minimum.
Noiseis digital distortion, which increases the higher your ISO level is set. In a sense, noise comes from your sensor being too sensitive. To counteract noise,there are a few things to look at. The larger a camera’s sensor is, the more light it can read; the more light it can read, the lower you can set your ISO level, decreasing noise. Also look at the speed of your lenses; the faster light can travel through them, the more light can hit your sensor.
This balancing act between capturing the light you want in your image and noise is called your “Signal-to-noise ratio”. Simply put, it’s the ratio between the detail in your image you wantto see, and the artifacts (noise, distortion) you don’t.
Summary
As a rule of thumb, the lower you can set your ISO, the better. This is unless you’re looking to have noise in your image as a visual choice.