The Exposure Triangle Explained: Aperture, Shutter and ISO

The exposure triangle is the three settings that decide how bright your shot is: aperture, shutter speed and ISO. Change one and you have to change another to keep the same brightness. Every one of those trades also changes the look, which is the part most guides skip.

This guide works in stops, the one unit all three settings share. It covers the twist video adds, lets you try every trade in a simulator, and ends with five films that pushed one side of the triangle as far as it would go.

What Is the Exposure Triangle?

The exposure triangle is a way of picturing how aperture, shutter speed and ISO balance each other to reach one exposure. Open the aperture a stop and the picture gets twice as bright. Make the shutter a stop faster and you are back where you started.

The idea comes from photographer Bryan Peterson’s book Understanding Exposure, first published in 1990. In that first edition the third side was film, because you changed sensitivity by loading a different stock. It became ISO in the 2004 second edition, after digital cameras made sensitivity a dial.

Each side does two jobs. That is what makes the triangle worth learning.

Setting	What it controls for brightness	What it changes in the look
Aperture	How wide the lens opens	Depth of field, from soft backgrounds to deep focus
Shutter speed	How long each frame collects light	Motion blur, from smeared to frozen
ISO	How much the signal is amplified	Noise and grain, from clean to speckled

Critics point out that ISO is not really part of exposure. Exposure is the light that reaches the sensor, and only the aperture, the shutter and the scene control that. ISO is gain applied afterward, like turning up a volume knob. The triangle is still the fastest way to learn the trades, as long as you remember that ISO brightens the picture without adding any light.

Stops: The Unit That Ties It Together

A stop is a doubling or halving of light, and it is the one unit all three sides share. That is why the trades work. One stop of aperture can be swapped for one stop of shutter or one stop of ISO, and the brightness stays the same.

The numbers look random until you know the pattern.

• Aperture: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. Each step multiplies the f-number by about 1.4 and halves the light. Smaller numbers mean a wider opening.
• Shutter speed: 1/30, 1/60, 1/125, 1/250, 1/500. Each step halves the time the sensor is exposed.
• ISO: 100, 200, 400, 800, 1600, 3200. Each doubling is one stop brighter.

So f/2.8 at 1/125 gives the same exposure as f/2 at 1/250 or f/4 at 1/60. Photographers call this reciprocity.

How bright is the world in stops? Bright sun with crisp shadows sits around exposure value (EV) 15 at ISO 100. That is where the old sunny 16 rule comes from: on a sunny day, set f/16 and a shutter of one over your ISO, so 1/125 at ISO 100. A street at night can be 9 or 10 stops darker than that. Every one of those stops has to come from somewhere on the triangle.

The Three Sides of the Triangle

Aperture

The aperture is the opening in the lens. Open it up (a lower f-number) and more light gets in, but the zone in focus gets thinner. Stop it down and more of the frame is sharp, but you need more light. Our guide to aperture and depth of field goes deeper, and the bokeh effect covers the soft background you get wide open.

Cinema lenses are marked in T-stops instead of f-stops. A T-stop measures the light the lens actually lets through, so it is always a slightly bigger number than the f-stop.

Shutter Speed

Shutter speed is how long each frame collects light. A slow shutter lets in more light and smears anything that moves. A fast one freezes motion but needs more light. Video measures it as a shutter angle too. Our guide to shutter speed explains both.

ISO

ISO sets how much the camera amplifies the signal from the sensor. The sensor collects the same light at ISO 100 and ISO 6400. The higher setting just turns up the gain, which also turns up the noise hiding in the shadows.

Every camera has a base ISO, the setting with the least added gain and the most dynamic range. Some have two. On these dual base ISO cameras, the second base uses a different circuit that keeps the shadows cleaner than plain gain would.

The Exposure Triangle in Video

In video, the shutter is the side you are not supposed to touch. Most crews keep it near a 180 degree shutter angle, which is 1/48 second at 24 fps, or 1/50 on most cameras. That keeps motion blur looking the way audiences expect from film. Our guide to the 180 degree rule shows why.

That leaves a problem on a bright day. A photographer would speed up the shutter. A video shooter puts a neutral density (ND) filter in front of the lens instead. ND is dark glass that cuts light evenly, without changing the color, the depth of field or the motion blur.

ND is labeled in density, and every 0.3 is one stop.

So the video triangle really has four sides: aperture, a locked shutter, ISO and ND. Pick the aperture for the look you want. Set ISO at or near the camera’s base. Then let ND or more light make up the rest.

Try the Exposure Triangle Yourself

Hold Exposure starts on ISO. Drag the aperture or the shutter and the camera moves ISO to keep the picture correctly exposed, the way auto ISO would. Switch it to Shutter or Aperture to see a different side do the balancing.

Setup 1: A Street at Night

f/2.8, 1/50 and ISO 800 put the night street right on the meter. Open up to f/1.4 and you could drop to ISO 200 for a cleaner image, but the street behind the actor melts into bokeh. Load the night street

Setup 2: Bright Day, Video Rules

Midday sun at f/2.8 and 1/50 is about six stops too bright, even at ISO 100. Add ND 1.8 and you keep the shallow focus and the film shutter. Load the bright day

Setup 3: Freeze the Action

A 1/1000 shutter freezes the passing car. At night that costs four and a third stops compared with 1/50, so the lens opens to f/1.4 and ISO climbs to 3200. Load the frozen car

How DPs Read Exposure on Set

Cinematographers rarely trust the camera’s own meter. Many start with a handheld incident meter, which reads the light falling on the actor’s face, and set the T-stop from the key light.

On a digital set, the monitor tools do the rest. Zebras paint stripes over anything near clipping. A waveform plots brightness across the frame. False color paints each brightness band in its own color, with green for middle gray and red for blown-out whites, though the colors vary by brand.

5 Films That Pushed the Exposure Triangle

Most films keep all three sides in a comfortable range. These five pushed one of them to the edge, and you can see the choice on screen. Stanley Kubrick famously did it on Barry Lyndon, shooting candlelit scenes with Zeiss 50mm f/0.7 lenses originally built for NASA, but that film earns its place on our lighting guide.

5) Zodiac (2007)

Zodiac shot its night murders with the lens wide open, so darkness swallows everything outside the light.

Zodiac was shot on Thomson Viper cameras recording uncompressed digital files. Savides often added ND so he could keep the lens wide open and the depth of field shallow. For the taxi murder, shot against a bluescreen over about three nights, Fincher told American Cinematographer that Savides was “shooting a little under, at about a T1.4 with a T1.6 prime.”

The result is a city that feels empty. Streetlight lands on the cab and the cab alone. Savides judged the exposure on calibrated monitors more than on a light meter.

4) Eyes Wide Shut (1999)

Eyes Wide Shut lit its Christmas parties with the Christmas lights themselves, then pushed the film two stops to see them.

On film, raising the ISO means pushing: underexposing the negative and developing it longer at the lab. Smith told American Cinematographer that the crew decided to shoot nearly all of the picture at T1.3 on Zeiss Super Speed lenses. Deluxe in London push-processed the whole film two stops, day exteriors included, so every scene would match.

That push is where the film’s soft, glowing grain comes from. The Ziegler party and the Sonata Cafe jazz club were lit almost entirely by practical bulbs in the shot. Kubrick considered bringing back the f/0.7 lenses from Barry Lyndon, but turned them down because they did not suit Steadicam or wide-angle work.

3) Miami Vice (2006)

Miami Vice used early HD cameras to see something film could not: the night sky over the city.

On these cameras gain is measured in decibels, and +6dB is about one stop. Beebe told American Cinematographer he kept the gain at +3dB most of the time and aimed his night exposures at 30 to 40 percent on a handheld waveform, which he used in place of a light meter. HD clipped highlights sooner than film, so he kept only about a stop of room above them.

The payoff was the sky. Shot on film at 24 fps, a city sky at night goes black. On the Viper it held detail, and the night sky shows up behind Crockett and Tubbs again and again. In the Dominican Republic, the crew ran big lamps on just one or two bulbs each because the cameras needed so little light.

2) The Creator (2023)

The Creator shot a big studio sci-fi film on a small Sony camera, and its low-light sensitivity shaped whole scenes.

Soffer told British Cinematographer that the crew “shot that entire sequence at 12,800 ISO,” lit mostly by the city around them. He pointed out that most cinema cameras top out around ISO 3200. The FX3’s second base sensitivity sits at 12,800, which is where the crew set it.

The same sensitivity bought the crew 15 to 20 extra minutes of usable dusk each day, and the opening beach assault was shot in those stretched evenings. For moonlight, Soffer set LED lights about a quarter of a mile from the set. Not every scene used the FX3: work on the LED volume at Pinewood used the bigger FX9.

1) Nope (2022)

Nope shot its night scenes in full daylight with an infrared camera, and stepped around the exposure triangle completely.

Lighting a whole valley at night was impossible, so van Hoytema shot the night scenes in sunlight. One camera recorded infrared, where a sunny landscape turns bright and the sky goes black. The film camera, lined up to see the same frame through matched lenses, captured the color. Colorist Greig Fisher at Company 3 blended the two into night.

Van Hoytema told Kodak the result looked “entirely plausible.” He first tested the idea on Ad Astra. On Nope it let horses run through a dark valley that no lamp could have lit. It is the strongest answer yet to the oldest problem in exposure: there is never enough light at night.

FAQs About the Exposure Triangle

The Final Cut on the Exposure Triangle

The exposure triangle is less a rule than a budget. Light is the money, and every stop you spend on depth of field or a frozen moment has to come from somewhere else. Zodiac spent it on darkness, Eyes Wide Shut on grain, and Nope found a way around the bill.

Start with the look. Pick the aperture for the focus you want and keep the shutter near 180 degrees. Then let ISO, ND and your lights settle the rest.

Which side of the triangle do you push first on your own shoots?