Learning about exposure: Part 1 — ISO

When someone asks me about exposure, I tell them how ISO, Shutter Angle, and Fstop affect the light that reaches the sensor. In essence, they all do the same thing. Move one, and it either makes the image brighter or makes it darker and then I detail each one.

Today we are going o Learn about ISO, what it does, how it does it, and other things to consider when adjusting it.

First, ISO is directly connected to Dynamic Range. Cinema Cameras have a native ISO, which became a thing when Digital cinema cameras gained popularity. If you increase your ISO, you increase your dynamic range in the highlights; if you lower it, you increase your dynamic range in the shadows. Every Cinema Camera (Alexa, Red, Blackmagic) has a native ISO, which means that the dynamic range in the highlights and shadows is optimal and balanced. A middle point, if you will. Each camera has several stops in the dynamic range and will vary from camera to camera.

What is Dynamic Range?

Dynamic range refers to how a camera can successfully capture the lightest and darkest areas of an image without losing detail. Once this range is exceeded, the highlights will wash out to white, and the darks will turn to black blobs.

Whenever you adjust your ISO, you move those stops of the dynamic range around, lower the ISO, and move 1–2 steps of the dynamic range to the shadows. Raise your ISO, and you move a few stops of dynamic range to the highlights losing them in the shadows.

Increasing your ISO will also add digital gain/grain to your image, mainly in the shadows/blacks. Lowering your ISO will clean up your shadows/blacks and limit your highlight dynamic range by a few stops, and highlights will blow out more quickly.

Most cameras have a native ISO of 800, like the Alexa and the Red cameras. Some Blackmagic cameras also have 800 as their native ISO, but the newer models like the Blackmagic Pocket Cinema Camera 4k-6k have a native ISO of 400. Each camera will have its own native ISO, and most of the time, it will be stated on their website.

What does it all mean?

Well, it means that you will achieve the best quality with the native ISO. If you see behind-the-scenes footage of tv shows or films…