ISO is one of the three fundamentals of photography (the other two are aperture and shutter speed). Whether you shoot with an iPhone or a DSLR, knowing how ISO works is important for taking good pictures.
Before we go any further, you should first understand the concept of exposure.
What is ISO?
In simple words, ISO is the level of sensitivity of the camera to light. The component within your camera that can change sensitivity is called “sensor”. It is the most important (and most expensive) part of a camera, and it gathers light and transforms it into an image.
The lower the ISO number, the less sensitive the sensor is to the light. A higher ISO number increases the sensitivity of your camera. The good part of increasing light sensitivity is that the photo gets brighter. The bad part is that you’re also increasing the noise. So the higher the ISO setting you use, the “noisier” the photo will be.
The typical ISO sequence is: 100, 200, 400, 800, 1600, 3200 and etc. Each step between two numbers doubles the sensitivity of the sensor. For example, ISO 200 is twice as sensitive as ISO 100, and ISO 400 is twice as sensitive as ISO 200! As the sensor is more sensitive to light, you can shoot at higher shutter speeds.
Controlling ISO on your iPhone
Because the iPhone camera has fixed aperture, you can only adjust shutter speed and ISO to control exposure. The native iPhone camera shoots in auto mode, so you need to download a professional camera app (such as Camera+) to control ISO and shutter speed.
When you get a chance, snap some pictures in bright sunlight and check the EXIF data. What you can see is that most of the photos have low ISO values (from ISO 25 to ISO 100). Why? The iPhone camera is optimised to shoot at a low ISO number and a higher shutter speed. Even the shutter speed gets slow, ISO keeps at a low value by default (e.g. ISO 25/1000s, ISO 25/500s, ISO 25/250s, ISO 25/125s, etc.). Until the shutter speed is too slow to get a crisp photo (i.e. 1/60s, 1/30s, 1/15s), ISO begins to increase. The ISO can go all the way up to ISO 2000. As ISO increases, so does the noise level. Low ISO numbers create low-noise photos, while high ISO numbers create high-noise photos.
As much as I love my iPhone, it isn’t a full-frame DSLR. This is what you can do to have low-noise photos:
1. Use the native camera: shoot in bright light conditions, and don’t blow out highlights or lose shadow details;
2. Use an advanced camera: shoot at low ISO and shutter speed with a tripod.