Exposure
Written by Abin Alex and Anu Joseph.
Abstract
Exposure is the total light a sensor collects for one picture, set by aperture, shutter speed and ISO and measured in stops, where one stop means twice the light or half of it. This guide sets out the exposure triangle, the exposure modes from automatic to manual, and exposure compensation, and it shows how to balance the three settings for the same exposure. It also explains how cinema crews control exposure when the shutter is fixed, using lighting, lens T-stops and ND filters. It is written for photographers and cinematographers.
Keywords: exposure; exposure triangle; stop; exposure modes; exposure compensation
- What is exposure?
- What are underexposure, overexposure and correct exposure?
- What is the exposure triangle?
- What is a stop of light?
- How do I balance aperture, shutter speed and ISO for the same exposure?
- What are the automatic and scene modes?
- What are Aperture Priority, Shutter Priority and Program modes?
- What are Manual, Bulb and custom modes?
- Which exposure mode should I use?
- What is exposure compensation, and when do I use it?
- What is exposure bracketing?
- What is HDR photography, and how does bracketing help?
- How is exposure controlled in cinematography?
- Which exposure mode suits each kind of photography?
What is exposure?
Short answer. Exposure is the total light the sensor collects for one picture, and it decides how bright or dark the picture looks. Three things control it: the size of the lens opening (aperture), how long the shutter stays open (shutter speed), and how bright the scene is. ISO is separate. It sets how the camera records the light that arrived.
- More light on the sensor gives a brighter picture. Less light gives a darker picture.
- Exposure is the light falling on the sensor multiplied by the time it falls: a bright light for a short time can equal a dim light for a long time.
- You control the light with aperture and shutter speed, and the way it is recorded with ISO.
- Photographic exposure also means the finished brightness of a picture, which you can change again in editing.
- The light from a lamp or a flash falls quickly with distance. Double the distance and the light on the subject drops to a quarter, which is two stops. The sun is so far away that moving a few metres changes nothing.
A simple picture to remember: a tap filling a bucket. The width of the tap is the aperture. How long the tap runs is the shutter speed. The water is the light. Different taps and different times can fill the bucket equally full.
Cham tipExposure is the amount of light that reaches the sensor. Check the picture and the histogram, not only the screen brightness.
Cham taskTake one picture too bright, one too dark and one correct. Describe each.
Check yourself: Name the two settings that control how much light reaches the sensor.
Aperture, which sets the size of the opening, and shutter speed, which sets how long it stays open.
What are underexposure, overexposure and correct exposure?
Short answer. Underexposure means too little light reached the sensor, so the picture comes out dark. Overexposure means too much reached it, so the picture comes out bright. A correct exposure keeps detail in both the shadows and the highlights. Detail lost in very bright areas cannot be recovered.
- Underexposed pictures look gloomy and lose detail in the shadows. Black areas with no detail are called blocked shadows.
- Overexposed pictures look washed out. White areas with no detail are called blown out highlights or clipped whites.
- Correct exposure is balanced: the important highlights and shadows both show detail.
- Exposure is measured in stops. Your light meter shows 0 for the exposure the camera thinks is correct, with minus numbers darker and plus numbers brighter.
- There is no single perfect exposure. A silhouette is deliberately dark, and a high key portrait is deliberately bright.
- A small deliberate underexposure, about one stop, can deepen colour. A small overexposure gives a paler, softer look.
| Exposure | Light on the sensor | Result |
|---|---|---|
| Underexposed | Too little | Dark picture, blocked shadows |
| Correct | Balanced | Detail in shadows and highlights |
| Overexposed | Too much | Bright picture, clipped highlights |
Table 1. Three results of exposure.
Cham tipDark areas lose detail when underexposed and bright areas lose detail when overexposed. Protect the highlights first.
Cham taskShoot an under, an over and a correct exposure. Compare them in the histogram.
Check yourself: Which can you not recover in editing, clipped highlights or slightly dark shadows?
Clipped highlights. They hold no detail to bring back, while slightly dark shadows can often be lifted, with some noise.
What is the exposure triangle?
Short answer. The exposure triangle shows how aperture, shutter speed and ISO depend on each other. The aperture sets how much light comes in, the shutter speed sets how long it comes in for, and ISO sets how strongly the signal is amplified. If you change one, you must change another to keep the same brightness. Each one also gives the picture its own look.
- Aperture: the size of the opening in the lens. It also controls depth of field.
- Shutter speed: how long the sensor is exposed. It also controls motion blur.
- ISO: how much the sensor signal is amplified. It also controls noise.
- Like the three legs of a stool, each matters. If you change one, you must adjust another.
- Two people shooting the same scene can choose different corners of the triangle and make different pictures at the same brightness.
| Setting | Controls | Also changes |
|---|---|---|
| Aperture | Amount of light | Depth of field |
| Shutter speed | Time the light enters | Motion blur and sharpness |
| ISO | Boost given to the signal | Noise |
Table 2. What each corner controls.
Cham tipThe triangle is aperture, shutter speed and ISO. Each has a side effect: depth of field, motion and noise.
Cham taskDraw three rows and write what each setting changes besides brightness.
Check yourself: Each corner of the triangle changes exposure and one other thing. What does shutter speed also change?
Motion blur, how still or moving things look.
What is a stop of light?
Short answer. A stop is a step of exactly double or half the light. Go up one stop and the sensor receives twice as much light. Go down one stop and it receives half as much. The aperture, the shutter and the ISO all use this same step, so a change on one dial can be cancelled on another. A stop is a relative change, not a fixed amount of light.
- Adding one stop doubles the light. Removing one stop halves it.
- Full aperture stops: f/1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32. Each is about 1.4 times the one before, because light depends on the area of the opening.
- Full shutter stops: 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30 s and so on. Each is twice or half the one before.
- Full ISO stops: 100, 200, 400, 800, 1600, 3200 and so on. See the ISO guide.
- Cameras also use third stops for finer control. Three third stops make one full stop.
- The word stop comes from early lens stops, metal plates with round holes slid into the lens to stop part of the light. The Waterhouse stop, invented by John Waterhouse of Yorkshire, is the best known (The Henry Ford, n.d.).
Präkel explains why stops appeared. Early plates and films were so slow that photographers used time alone to set the exposure. As materials became faster, controlling the intensity of the light as well gave more flexibility (Präkel, 2009).
| Setting | One stop brighter | Starting point | One stop darker |
|---|---|---|---|
| Aperture | f/2.8 | f/4 | f/5.6 |
| Shutter speed | 1/125 s | 1/250 s | 1/500 s |
| ISO | 400 | 200 | 100 |
Table 3. One stop on each scale. Change only one setting at a time.
Cham tipOne stop is twice the light or half the light.
Cham taskCount the stops from f/2 to f/8.
Check yourself: Going from f/5.6 to f/4, how much more light enters?
Twice as much, one stop.
How do I balance aperture, shutter speed and ISO for the same exposure?
Short answer. Count in stops. Whatever extra stop you give with one setting, take back with another. Opening the aperture by two stops needs a shutter two stops faster, for example. Many combinations give the same brightness, but each gives a different picture. ISO is the odd one out, because it changes how the light is recorded, not how much arrives.
- The light that arrives on the sensor depends on the scene, the aperture and the shutter speed. ISO then sets how strongly the camera boosts the signal.
- That is why raising ISO makes the picture brighter even though no more light has entered. See the ISO guide.
- Swap stop for stop. Close the aperture by one stop and slow the shutter by one stop, or raise the ISO by one stop and speed the shutter up by one stop.
- Every combination in the table below gives about the same brightness.
- Choose the setting that matters most for your picture first, then balance the rest. Shutter speed for motion, aperture for depth, and ISO for the rest.
| Aperture | Shutter speed | ISO | Compared with the reference |
|---|---|---|---|
| f/4 | 1/125 s | 100 | Reference |
| f/5.6 | 1/60 s | 100 | Aperture one stop darker, shutter one stop brighter |
| f/2.8 | 1/250 s | 100 | Aperture one stop brighter, shutter one stop darker |
| f/4 | 1/250 s | 200 | Shutter one stop darker, ISO one stop brighter |
| f/8 | 1/125 s | 400 | Aperture two stops darker, ISO two stops brighter |
Table 4. Equal exposures. Each row gives the same brightness as the reference.
Cham tipMake one change, then undo it with another. Open the aperture one stop and speed up the shutter one stop.
Cham taskStarting at f/4, 1/125 s and ISO 400, write three other settings with the same exposure.
Check yourself: f/4, 1/125 s, ISO 100 is correct. You change to f/8. What shutter speed keeps the brightness at ISO 100?
1/30 s. f/8 is two stops less light, so the shutter must be two stops slower.
What are the automatic and scene modes?
Short answer. In Auto the camera picks the aperture, shutter speed, ISO and flash. Scene modes such as Portrait, Landscape, Macro, Sports, Night Portrait and Food do the same, with the settings tuned to that subject. They are quick and fine when you are starting out, but they leave you little control.
- Auto mode: the camera decides everything. Good when you are new, or must shoot quickly.
- Portrait mode favours a wide aperture for a soft background.
- Landscape mode favours a smaller aperture so more of the scene is sharp.
- Sports mode favours a fast shutter speed to freeze action.
- Macro, Night Portrait, Food and Flash Off modes also adjust settings for their purpose.
- The camera may also change colour, contrast and flash, so results can differ between cameras.
Cham tipAutomatic modes are fine for learning composition, but they hide the settings. Check what the camera chose after each shot.
Cham taskTake a shot in Auto. Look up the aperture, shutter speed and ISO the camera used.
Check yourself: Which settings does the camera choose in Auto mode?
Aperture, shutter speed, ISO and flash.
What are Aperture Priority, Shutter Priority and Program modes?
Short answer. With Aperture Priority (A or Av) you pick the aperture and the camera picks the shutter speed. With Shutter Priority (S or Tv) you pick the shutter speed and the camera picks the aperture. With Program (P) the camera picks both, and you can shift the pair while the exposure stays the same. All three read the exposure from the camera's meter.
- Aperture Priority: you set the aperture for depth of field, the camera sets the shutter speed.
- Shutter Priority: you set the shutter speed for motion, the camera sets the aperture.
- Program: the camera sets shutter speed and aperture to match the subject brightness, and you can still choose focus, metering and other settings.
- Program shift: you turn a dial after a half press of the shutter button to change the aperture and shutter pair while the exposure stays the same.
- The ISO is set by you, or by Auto ISO.
- If the camera cannot reach the exposure, for example the shutter speed it needs is slower than the lens allows, the displayed value blinks as a warning on many cameras. Check your manual.
| Mode | Letter | You set | Camera sets |
|---|---|---|---|
| Aperture Priority | A or Av | Aperture | Shutter speed |
| Shutter Priority | S or Tv | Shutter speed | Aperture |
| Program | P | Nothing needed | Aperture and shutter speed |
Table 5. The priority modes.
Cham tipUse Aperture Priority when depth of field matters and Shutter Priority when motion matters.
Cham taskShoot a portrait in Aperture Priority and a moving subject in Shutter Priority.
Check yourself: You want to freeze a running dog. Which priority mode do you choose?
Shutter Priority (S or Tv), with a fast shutter speed.
What are Manual, Bulb and custom modes?
Short answer. Manual (M) leaves aperture, shutter speed and ISO to you, and the camera only shows a meter reading as a guide. Bulb (B) holds the shutter open for as long as you keep the button pressed, which suits very long exposures. Custom modes (C1, C2, C3) save your own settings so you can recall them in one step.
- Manual mode gives full control and the same exposure from shot to shot. It is the standard for studio work, flash and video.
- In Manual the meter still shows whether you are bright, dark or about right, and you adjust until it reads close to zero.
- Bulb mode is a type of Manual mode where the shutter stays open while you hold the button. Use a tripod, and a remote release if you can.
- Custom modes C1, C2 and C3 hold three sets of your own settings, for example one for portraits and one for action.
- Many cameras remember the custom settings even after you turn the camera off, but check your manual.
Cham tipUse Manual when the light is steady. Use Bulb for exposures longer than your camera's longest timed speed.
Cham taskOn a tripod, try a ten-second Bulb exposure of a night scene.
Check yourself: What does Bulb mode do?
It keeps the shutter open as long as you hold the button down.
Which exposure mode should I use?
Short answer. Begin with Aperture Priority. It gives you control of depth of field, the effect beginners notice most, and the camera handles the rest. Switch to Shutter Priority when motion matters most. Use Manual when you need the same exposure from shot to shot, as in studio work, flash and video. Program suits quick, simple pictures.
- Portraits, landscapes and still life: Aperture Priority.
- Sports, wildlife and moving traffic: Shutter Priority, or Manual with Auto ISO.
- Studio, flash, video and consistent series: Manual.
- Quick snapshots in changing light: Program or Auto.
- Whatever the mode, check the picture and the meter, and correct with exposure compensation.
| Situation | Mode | Why |
|---|---|---|
| Portrait with a soft background | Aperture Priority | You control depth of field |
| Running child or bird | Shutter Priority | You control motion |
| Studio flash, video, series of pictures | Manual | Same exposure every time |
| Quick snapshots | Program or Auto | Fastest |
Table 6. Choosing a mode.
Cham tipChoose the mode by what matters most: depth of field, motion or full control.
Cham taskWrite which mode you would use for a portrait, a cricket match and a night sky.
Check yourself: Which mode gives the same exposure every time you press the button, whatever the scene?
Manual.
What is exposure compensation, and when do I use it?
Short answer. Exposure compensation tells the camera to make its automatic exposure brighter or darker. A plus setting brightens the picture and a minus setting darkens it. It is counted in EV, where 1 EV equals one stop, and most cameras step in thirds of a stop. Use it when the camera is fooled, for example by snow, a bright sky or a black cat.
- Exposure compensation adjusts the exposure the meter suggests, in stops. 1 EV is one stop, so +1 doubles the exposure and -1 halves it.
- Plus gives a brighter picture, minus a darker one, usually in third stop steps.
- It works in Program, Shutter Priority, Aperture Priority and Manual modes on Canon cameras (Canon, n.d.-b).
- In Aperture Priority the camera changes the shutter speed. In Shutter Priority it changes the aperture. In Manual with Auto ISO, many cameras change the ISO instead.
- The setting stays on after you turn the camera off, on Canon cameras, so reset it to zero when you finish (Canon, n.d.-b).
- Meters aim for a middle grey, so a bright scene such as snow or sand often needs plus compensation, and a dark scene needs minus.
| Scene | Compensation | Reason |
|---|---|---|
| Snow, beach, white wall | Plus 1 to plus 2 | The meter makes bright scenes too grey |
| Dark subject on a dark background | Minus 1 | The meter makes dark scenes too bright |
| Bright sky behind a person | Plus 1 | Meter is led by the sky |
| Highlights blinking in the picture | Minus 1 | Protects detail in the highlights |
Table 7. Typical exposure compensation, in EV. Starting points only.
Cham tipIf the scene is mostly white, add plus compensation. If it is mostly dark, add minus.
Cham taskPhotograph a white wall at 0 and at plus 1 compensation. Compare.
Check yourself: A snow scene looks grey in Aperture Priority. Which way do you move compensation?
Plus, for example plus 1 EV, to make it brighter.
What is exposure bracketing?
Short answer. Bracketing is taking several pictures of one scene at different exposures, usually one normal, one darker and one brighter. You choose the best frame afterwards, or blend them. Many cameras can do it automatically with AEB, short for Auto Exposure Bracketing. It is a safe way to get a good exposure in a difficult scene.
- On a typical Canon camera, AEB takes three shots in the order standard, darker, brighter (Canon, n.d.-a).
- The range can be up to plus or minus 3 stops, in third stop steps (Canon, n.d.-a).
- A good start is three shots, one stop apart. For very high contrast, try five shots, one to two stops apart.
- Hold the camera on a tripod and use a drive mode that takes all frames at once.
- On Canon cameras, AEB is not available with flash or bulb exposures (Canon, n.d.-a).
- Bracket with shutter speed when you can, so depth of field stays the same.
| Bracket | Shots | Step | Use |
|---|---|---|---|
| Standard | 3 | 1 EV | Most scenes |
| Wide | 5 | 1 to 2 EV | Very high contrast, sunrise or sunset |
| Fine | 3 | 1/3 EV | Check the best exposure of a difficult scene |
Table 8. Bracketing choices.
Cham tipWhen you cannot judge the light, bracket three shots, for example minus 2, 0 and plus 2 EV.
Cham taskUse auto exposure bracketing on a window scene and compare the three frames.
Check yourself: In what order does a typical AEB take its three shots?
Standard exposure, darker, then brighter.
What is HDR photography, and how does bracketing help?
Short answer. HDR stands for high dynamic range. Bracketed pictures are blended so that the dark areas come from the bright frame and the bright areas from the dark frame, and the result holds more detail than any single frame. It suits landscapes, sunsets and interiors with bright windows. A tripod and a still scene give the cleanest result.
- Take a bracketed set, at least three frames, with a tripod.
- Merge them in editing software, or with the camera's HDR mode.
- Each part of the picture is taken from the frame where it is best exposed.
- Moving subjects such as clouds, water or people can leave ghost edges.
- Do not push it too far. Heavy HDR often looks unnatural.
- Modern cameras and RAW files already hold a lot of range, so use HDR only when one frame cannot hold the whole scene.
Cham tipUse a tripod for HDR so the frames line up, and avoid moving subjects.
Cham taskBracket a bright window or a sunset and merge the frames in an editor.
Check yourself: Why do you use a tripod for HDR?
So the frames line up when they are merged.
How is exposure controlled in cinematography?
Short answer. Cinema exposure is mostly decided in advance. The shutter angle and frame rate are chosen for the look, so the crew sets exposure with lighting, the lens stop, ND filters and the camera's ISO or exposure index. Cinema lenses are marked in T-stops, which measure the light that actually passes through the lens, so one T-stop gives the same exposure on any lens.
- The shutter is normally fixed, for example at a 180 degree angle, so shutter speed is not used to balance exposure. See the shutter speed guide.
- T-stops measure the light actually transmitted by the lens. F-stops are a calculated value, so two lenses at the same f-stop can differ in real brightness.
- ND filters cut light by whole stops so you can keep the lens stop you want, for depth of field.
- Cameras are set to a base ISO or an exposure index. On Sony cinema cameras, changing the exposure index does not change the recording sensitivity (Sony, n.d.).
- Exposure is checked with a light meter, a waveform, false colour and zebras, not by eye.
- The lighting is changed to match: the DOP adds light or takes it away, instead of changing the settings.
| Tool | What it controls | Notes |
|---|---|---|
| Lens T-stop | Light through the lens, and depth of field | Real transmission, same on every lens |
| ND filter | Light, in whole stops | Keeps the lens stop you want |
| Lights | Light on the scene | The main exposure tool |
| Shutter angle | Motion blur | Fixed, not used for exposure |
| ISO or exposure index | How the camera records the light | Stay near the base value |
Table 9. The cinematographer's exposure tools.
Cham tipIn cinema, judge exposure with a waveform, false colour or light meter, not only the screen.
Cham taskExpose a face using zebra or false colour as described in your camera's manual.
Check yourself: Why do cinema lenses use T-stops instead of f-stops?
T-stops measure the light really transmitted, so the same T-stop gives the same exposure on every lens.
Which exposure mode suits each kind of photography?
Short answer. Choose the exposure mode by what you want to control. Aperture priority controls depth, shutter priority controls motion, and manual controls everything. Treat every line below as a starting point.
- Birds. Manual with Auto ISO, so the shutter speed and aperture stay fixed while the light changes. Add plus compensation against a bright sky.
- Animals and pets. Aperture priority outdoors. Manual with Auto ISO when the light changes quickly.
- Reptiles. Aperture priority on a tripod, because they stay still. Check the highlights on pale rock or sand.
- Insects and macro. Manual with flash, so the flash sets the exposure and the camera settings stay fixed.
- Portraits. Aperture priority. Use plus compensation when the background is bright.
- Fashion. Manual in the studio, so every frame has the same exposure.
- Wedding and events. Aperture priority, or manual with Auto ISO. Check the white dress for clipped highlights.
- Product. Manual on a tripod, so every frame matches.
- Automotive. Shutter priority for panning, so the speed stays fixed. Manual for studio and night work.
- Photojournalism. Aperture priority for speed, with exposure compensation in difficult light.
- Sports and action. Manual with Auto ISO, or shutter priority.
- Landscape. Aperture priority on a tripod. Manual when you bracket.
- Street and documentary. Aperture priority at f/8 with Auto ISO, or manual with settings fixed for the light.
- Night and astro. Manual, every time.
- Cinema. Manual. The shutter angle is fixed, and the exposure is set with the stop, ND filters and light.
Questions beginners ask
What is a stop in photography?
A stop is a step of double or half the light. It applies to aperture, shutter speed and ISO.
What is the correct exposure?
One that keeps detail in the parts of the picture that matter and gives the brightness you want. It is a choice as well as a measurement.
Which mode should a beginner use?
Aperture Priority. You control depth of field and the camera sets the shutter speed.
What does plus 1 exposure compensation mean?
It makes the picture one stop brighter than the camera would normally make it.
Why is my picture too dark when the meter says zero?
The meter aims for middle grey, so a bright scene can come out too dark. Add plus exposure compensation and check the picture. Read more in How Metering Works.
References
- Canon. (n.d.-a) Auto Exposure Bracketing (AEB). Canon EOS R Advanced User Guide. cam.start.canon/en/C011/manual/html/UG-05_Shooting-1_0060.html
- Canon. (n.d.-b) Exposure Compensation. Canon EOS R6 Advanced User Guide. cam.start.canon/en/C007/manual/html/UG-04_AF-Drive_0090.html
- Präkel, D. (2009) Basics Photography 07: Exposure. Lausanne: AVA Publishing. See the sections on stops (pp. 26–27), reciprocity and the inverse square law (pp. 28–29), and over- and underexposure (pp. 38–43).
- Sony. (n.d.) Using the Exposure Index in shooting. Cine EI mode help guide. helpguide.sony.net/di/pp/v1/en/contents/TP1000756720.html
- The Henry Ford. (n.d.) Waterhouse Lens Stops in Case, 1858-1870. thehenryford.org/collections/explore/artifact/480897
How to cite this guide. Alex, A., & Joseph, A. (2026). Exposure: A guide for photographers and cinematographers. Creative Hut Academy. https://creativehut.org/library/what-is-exposure/
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