What is ISO — Camera ISO and the Exposure Triangle Explained

Light is responsible for everything we see on the big screen. Spectacle. Magic. Just as often as cinematographer use light to tell a story, they also use darkness. To capture the range of human emotions through light and darkness, it is fundamental to understand the three components of the exposure triangle. Aperture, Shutter Speed, and today’s topic ISO.

“What Is ISO?”

So how does ISO work? Back when filmmakers shot exclusively on film different film stocks had different speeds or sensitivities to light. The film sensitivity is known as ISO. The term comes from the Greek “Isos”, meaning equal and is defined by the international organization for standardization (ISO). ISO sets various international standards for everything from country codes to medical devices. In today’s digital camera technology ISO is used for the sensitivity of a camera’s sensor, rather than film. Aperture and shutter speed, both physically control the amount of light let into the camera. In our previous episode on the exposure triangle, we discussed how aperture works, like the pupil of an eye. It closes to let in less light. Or opens to let in more light.

And the ISO controls how sensitive the camera’s sensor is to the light that hits it. Lastly, the shutter speed controls, how long light will hit the sensor. We’ll cover this in our next episode. Now, a lower ISO value makes the sensor less sensitive to light making the image darker. A higher ISO value makes the sensor more sensitive to light making the image brighter. When determining the exposure of a shot it is most common to adjust your ISO after your aperture. And shutter speed are set. So why would a cinematographer change their ISO? Let’s look at a couple of different scenarios starting with low light situations. The film “1917” spans various long takes to create an immersive 360-degree experience.

This meant that cinematographer, Roger Deakins had to light many of the darker scenes with practical lights, visible on screen… …while still retaining a deep focus. “- Look at this. He’s massive.” In other words, Deakins had to contend with less lighting and a closed aperture. Remember, to get a larger depth of field, you want to close your aperture as much as possible, but this means less light will enter your sensor. So to pull this off, he needed a camera that could handle extremely low light situations. The ARRI Alexa Mini LF. ” – Very thankful for this camera. Thank you very much. Certainly served our purpose very well. The LF I could rate it at 1600. Because there’s all the night scenes in the interiors. There’s quite a lot of footage at night in those little bunkers.” Because of this high ISO Deakins could light minimally while closing his aperture to achieve a larger depth of field. However, there is a side effect of increasing your ISO that every cinematographer should be aware of. Noise.

Increasing your ISO may help brighten up your shot, but there is a catch. If your ISO is too high, your camera sensor will become too sensitive and it will create noise and grain. Take this low light shot for example, this image is clearly underexposed. To properly expose the shot without compromising your aperture or shutter speed let’s try increasing our ISO. Notice how increasing the ISO value brightens up our shot, but also produces more noise. So how do you minimize noise? Get to know your camera. Every camera is a little different so understand its particular settings like its “Dynamic Range” and “Native ISO”. The dynamic range measures the limits of how dark and light an image can be without losing detail. So a larger dynamic range results in more detail and color range. Adjusting the ISO in either direction moves that range sacrificing either the highs or lows in the process. As a general rule, to shoot an image with less noise and greater range of color, you’ll want to shoot as close to as possible to what is known as a native ISO.

Every digital camera has a native ISO specific to that camera. For instance, the ARRI Alexa Mini’s native ISO is 800. Although many cinematographers strive for polished image, some filmmakers take advantage of green and noise because the texture can bring a unique quality to a shot. “- Film Photography is a chemical miracle. It always looks different. It always looks real. There’s grain. Number one. And the grain is always moving, it’s swimming, which means that even in a still life of, let’s say a flower that flowers alive even though it’s not moving because the film itself, the image is alive. And that’s the difference.” Spielberg is referring to film grain. Not digital noise. “- What are you doing? – I was filming this dead bird. – Why? – Because it’s beautiful.” Remember, there’s a clear difference between the two. An image captured on a film strip produces film grain during the chemical bath it takes when it’s been converted. “- You never quite know what you’re going to get after the film takes a bath and exposes the positive from the negative.”

This is not to be mistaken for noise, which is when ISO is pushed too far on a digital camera producing less desirable artifacts. However, some filmmakers intentionally use a high ISO value to create noise, to create an analog-style reminiscent of film green. Cinematographer Brandon Trost uses this quality in the film “The Disaster Artist”. “- Guys, this is real Hollywood movie. – Everyone set? – Yeah. – Ready. And, uh, action.” Trost shot the movie at 3,200 ISO and added additional green in post, purely for style. “- I think I don’t like things that look super nice. It gives you a variety, you know stuff that’s interesting texture stuff that you can like reach out and touch and that’s sort of what I’m always after a little bit.” Whether your cinematography style utilizes low or native ISO values for a polished look.

Or you’re looking to use higher ISO values to produce noise stylistically. “- Ha-ha-ha! What a story, Mark! – Cut!” Understanding ISO is crucial in achieving the shot you envision. And to fully understand ISO, you must learn how it works with aperture and shutter speed within the exposure triangle. In the description, you’ll find a link to download a free ebook on the exposure triangle. And how each of the three settings work in combination. Did any shots come to mind as we covered ISO? Share your favorites in the comments below. In the next episode, we’ll explore shutter speed and how it’s used to control light and motion. We’ve got new content every week.

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