Understanding ISO: It's Not Just Brightness

What is ISO?

In the film days, ISO referred to the physical sensitivity of the film stock to light. A higher number meant more sensitive chemicals, but also larger "grain."

In digital photography, ISO is simply amplification. You aren't making the sensor more sensitive; you are turning up the volume on the signal it receives.

The Dual Base ISO Revolution

Modern cameras often have "Dual Base ISO." This means they have two sweet spots where the noise is lowest. For example, the Sony FX3 might look cleaner at ISO 12,800 than it does at ISO 4,000.

When to Crank It

Don't be afraid of high ISO. A noisy photo is better than a blurry one. If you are shooting a moving subject in low light, prioritize your shutter speed. You can fix noise in post (hello, Lightroom Denoise), but you can't fix motion blur.

Summary

1. ISO amplifies the signal.
2. Higher ISO = more noise (usually).
3. Learny our camera's "Base ISO" values for the cleanest image.