What Is Aperture? F-Stops and Depth of Field in 7 Movies

What is aperture? It is the opening inside your lens that lets light reach the sensor. Make it wider and more light gets in. Make it smaller and less does. That one ring on the lens also decides how much of your shot is sharp, which makes aperture as much a storytelling tool as an exposure setting.

This guide covers how aperture works, how to read f-stops, why cinema lenses are marked in T-stops, and how depth of field changes what an audience sees. Then come 7 movies that use focus to tell the story, ranked by how much the meaning of the scene depends on what is sharp and what is not. For the bigger picture, start with our cinematography guide for beginners.

What Does Aperture Do?

Aperture does two jobs at once.

• It sets exposure. A wider opening lets in more light, so the image gets brighter.
• It sets depth of field. A wider opening also shrinks the zone that looks sharp.

You cannot change one without the other. That is why a cinematographer picks an aperture for the look first, then fixes the brightness with lights, ND filters or ISO.

Is aperture the same as shutter speed? No. Aperture is how wide the opening is. Shutter speed is how long the sensor collects light for each frame. Together with ISO they make up the exposure triangle.

F-Stops Explained

An f-stop is the number that tells you how wide the aperture is. It is the focal length of the lens divided by the width of the opening. A 50mm lens with a 25mm opening is at f/2. Close the opening to about 6mm and you are near f/8.

That is why the numbers run backwards. A small f-number means a big opening.

Each full stop halves or doubles the light. Go from f/2.8 to f/4 and you cut the light in half. Go from f/2.8 to f/2 and you double it.

F-stop	Opening	Light vs one stop wider	Typical use on set
f/1.4	Very wide	Most light	Night exteriors, low light, a face isolated from the room
f/2	Wide	Half of f/1.4	Close-ups with a soft background
f/2.8	Wide	Half of f/2	Interviews and handheld scenes
f/4	Medium	Half of f/2.8	Two-shots that keep both actors sharp
f/5.6	Medium	Half of f/4	Medium shots, a lens’s sharpest range
f/8	Narrow	Half of f/5.6	Wides and groups
f/11	Narrow	Half of f/8	Bright day exteriors, deep focus
f/16 to f/22	Very narrow	Half again per stop	Rarely on purpose. Images start to soften

Is f/2.8 a high or low aperture? It is a wide aperture with a low f-number. People mix up “high” and “low” all the time, so say “wide” and “narrow” on set and nobody gets it wrong.

Is it better to have a higher or lower f-number? Neither. Lower gives you more light and blur. Higher gives you more of the frame in focus. Pick the one the shot needs.

Here is a quick video that shows aperture at work.

F-Stop vs T-Stop

An f-stop is math. A T-stop is a measurement.

The f-stop comes from the size of the opening alone. But every piece of glass inside a lens soaks up a little light. A T-stop (the T stands for transmission) measures how much light actually reaches the sensor. So a lens marked f/1.4 might really pass the light of T1.5. The T-stop number is always a little higher than the f-stop.

Why do cinema lenses use T-stops? Because a film cuts between lenses all day. If your 35mm and your 85mm are both set to T2.8, the shots match in brightness. Set two still lenses to f/2.8 and one can come out a fraction darker, and the colorist has to fix it in every cut.

You will see T-stops on cinema primes and f-stops on most photo lenses. For depth of field, they behave the same way.

What Is Depth of Field?

Depth of field is the zone from near to far that looks sharp in your shot. Three things control it.

1. Aperture. Wider means shallower.
2. Focal length. Longer lenses look shallower than wide lenses at the same stop.
3. Distance to your subject. The closer you focus, the thinner the sharp zone gets.

Sensor size plays a part too. A bigger sensor needs a longer lens for the same framing, so it looks shallower at the same stop. That is one reason large format cameras get talked about so much.

	Shallow depth of field	Deep depth of field
What it looks like	Subject sharp, background soft	Near and far both sharp
Aperture	Wide, f/1.4 to f/2.8	Narrow, f/8 to f/16
Lens	Longer, 50mm and up	Wider, 35mm and down
Distance	Close to the subject	Further back
What it does	Tells the audience where to look	Lets the audience choose where to look

Shallow Depth of Field

Shallow focus pulls one thing out of the world. A face in a crowd, a hand on a gun, a letter on a desk. Everything else turns soft, so the audience has no choice about where to look.

The soft part has its own name. Bokeh is the look of that blur, and our bokeh guide covers the lenses and settings that shape it.

Deep Focus

Deep focus keeps the foreground, middle and background sharp at once. It needs a narrow aperture, a wide lens and a lot of light.

Cinematographer Gregg Toland made it famous in Citizen Kane (1941), shooting at deep stops so actors at the back of a room stayed as sharp as those at the front. Our guide to the establishing shot shows how wide, sharp frames set up a scene.

Deep focus hands control to the audience. Two things can happen in one frame, and the viewer decides which one to watch.

Rack Focus and the Split Diopter

Two tricks let you move or cheat depth of field.

• Rack focus. The focus shifts from one subject to another during the shot. The audience’s eye goes where the focus goes.
• Split diopter. A half-lens fitted in front of the main lens. One side of the frame focuses close, the other far. It fakes deep focus, with a soft line where the two halves meet. See 7 famous examples in our guide to the split diopter shot.

You will see both in the list below.

7 Depth of Field Examples in Movies

These 7 movies count down to a 1946 drama that hides its turning point at the back of the frame. Each one is ranked by how much the story depends on its focus choice. Four use deep focus, two use shallow focus, and one cheats.

7) Blow Out (1981)

Blow Out uses a split diopter to put a sound man and the sound he is chasing in focus at once.

John Travolta plays Jack, a sound effects man who records a car crash that turns out to be murder. In the park scene, Jack’s face fills one side of the frame while an owl he is recording sits sharp in the distance on the other. No lens could hold both in focus. The split diopter does.

De Palma uses the trick again and again, along with split screens and long tracking shots. Zsigmond kept the rest plain. “Basically I just shot Blow Out straight,” he said, and about seventy percent of the film was shot at night.

6) The Insider (1999)

The Insider uses razor-thin focus to make a whistleblower feel watched from every side.

Russell Crowe plays Jeffrey Wigand, a tobacco scientist deciding whether to go public. Mann and Spinotti frame him tight, often cutting off half his face, with the world behind him smeared into shapes he cannot read.

One critic wrote that the long lenses and “ultra-shallow depth of field” create “a visual equivalent to this constant apprehension.” The film earned 7 Oscar nominations, including Best Cinematography. Watch how often the focus slips. The audience never feels settled, and neither does Wigand.

5) The Master (2012)

The Master shot close-ups on 65mm film, where the focus is so thin that a face can drift out of it.

Anderson shot most of the film on 65mm, a format built for wide epics, then used it for faces. A bigger frame means shallower focus, and Photogénie notes a 300mm lens on most of the big close-ups. The dreamlike feel “depends on the severely limited depth of field.”

Focus puller Erik Brown worked largely by instinct, because the actors had little or no blocking. In one shot, the yacht where Freddie meets Dodd starts as “a defocused plane of glittering colour blots,” then racks into focus. Freddie sees the thing that will change his life before he understands it, and so do we.

4) Mank (2020)

Mank copied the deep focus of Citizen Kane, then learned to change its depth of field in the middle of a shot.

Mank tells the story of Herman Mankiewicz writing Citizen Kane, so Messerschmidt shot it the way Toland shot Kane. According to Leitz, the team “generally shot at T8, T11 and sometimes at T16” on Summilux-C lenses, mostly 21mm to 50mm.

The clever part is the Cinefade, a motorized variable ND filter. As it darkens, the iris opens to match, so the exposure stays the same while the depth of field shrinks. The look moves from T11 to T2 in one take, from a deep, busy room to a single face. Messerschmidt won the Oscar for Best Cinematography.

3) The Rules of the Game (1939)

The Rules of the Game keeps masters and servants sharp in the same frame, so their stories run side by side.

Renoir wanted the backgrounds of his country house farce sharp, so he “ordered some special lenses, very fast lenses, but ones that still gave us considerable depth, so that we could keep our backgrounds in focus almost all the time.” Guests flirt in the foreground while servants scheme behind them, and you can watch both.

The film flopped in 1939 and was banned in France soon after. Critics later rated it one of the best films ever made. It ranked second in the Sight and Sound poll in 1972, 1982 and 1992. Deep staging is the reason it rewards a second viewing.

2) The Zone of Interest (2023)

The Zone of Interest keeps everything in focus, including the Auschwitz camp behind the garden wall.

Camp commandant Rudolf Höss lives with his family in a house that shares a wall with the camp. Żal told British Cinematographer the lenses “allowed us to keep everything in focus, with everything stopped at 5.6,” and that “we didn’t want a shallow depth of field.”

So the guard towers and chimneys stay sharp behind every garden party. The family never looks at them. The audience cannot stop looking. It is the mirror image of Son of Saul, which hides the same camp in blur. Both choices work, and comparing them teaches more about depth of field than any chart. The film won the Oscars for Best International Feature and Best Sound.

1) The Best Years of Our Lives (1946)

The Best Years of Our Lives hides its turning point in a phone booth at the back of a deep-focus frame.

Three veterans come home from the war. In the famous bar scene, Homer and Butch play piano in the foreground. Al watches from the middle of the room. At the back, small and sharp, Fred calls Peggy from a phone booth to end their romance, a call Al asked him to make.

Critic André Bazin wrote that the true action “develops almost clandestinely in a tiny rectangle at the back of the room.” Toland’s deep focus is what makes it possible. A shallow lens would have forced a cut. Here you watch the piano, feel Al’s eyes and find the phone booth on your own. The film won seven Oscars, including Best Picture.

How to Choose an Aperture for Video

Start with the story, then deal with the light. Ask one question first: should the audience look at one thing, or choose between several?

• One thing. Open up to f/2 or T2 and get close.
• Several things. Stop down to f/5.6 or T5.6 and beyond, and step back with a wider lens.

Then lock your shutter. For natural motion, video keeps the shutter near 180 degrees, about 1/50 at 24 frames per second. You cannot raise the shutter speed to fix a bright day the way photographers do, so you control the light with ND filters instead. Our guide to the 180 degree rule covers the shutter side.

Watch the extremes. Most lenses look sharpest a couple of stops down from wide open. Wide open, edges can soften and colors can fringe. Past f/11 or so, diffraction starts to blur fine detail, more on small sensors than large ones.

Plan for focus. At T1.4 the sharp zone on a close-up can be a few inches deep. On a film set, the first assistant camera pulls focus on every take. On your own shoot, rehearse the move and put tape marks on the floor.

FAQs About Aperture

The Final Cut on Aperture

So, what is aperture? It is the opening in your lens that sets how much light gets in and how much of the shot is sharp. Lower f-numbers give you more light and shallower focus. Higher numbers give you less light and deeper focus. Cinema lenses use T-stops so the shots match.

Here is a drill for this week. Put two people in a room, one near the camera and one at the back. Shoot the scene once at T2 with focus on the front actor, then once at T8 with both sharp. Watch them back to back and ask whose story each version tells.

When you are ready to go further, see how a cinematographer makes these choices on set, how shot composition places people in depth, and which types of shots suit each lens.