Camera Basics and the Exposure Triangle: A Terminology Guide
Camera Basics and the Exposure Triangle: A Terminology Guide
The exposure triangle is three controls governing how much light reaches the image: aperture, shutter speed, and ISO. Changing any of them affects brightness and one other thing: aperture changes depth of field, shutter changes motion rendering, ISO changes noise. In video specifically, shutter speed stays locked to frame rate, so you control exposure with aperture, ISO, and filters.
What exposure actually is
Exposure is the amount of light reaching the camera's sensor. Too much and the image is blown out (overexposed); too little and it's dark (underexposed).
The three controls governing this are called the exposure triangle. It's a triangle because you can't change one without disturbing the balance — reduce light on one side and you must compensate on another.
Side one: aperture
Aperture is the width of the opening light passes through, measured as an f-number such as f/1.8 or f/8.
The rule that confuses beginners: a smaller number means a wider opening and more light. So f/1.8 is wider than f/8.
The side effect: depth of field — how much appears sharp in front of and behind your subject.
- Wide aperture (small number) = shallow depth of field = blurred background. Suits faces and interviews.
- Narrow aperture (large number) = deep depth of field = everything sharp. Suits wide landscapes.
Side two: shutter speed
Shutter speed is how long the sensor stays exposed to light, measured in fractions of a second such as 1/50 or 1/200.
- Slow shutter (1/30) = more light + extended, blurred motion.
- Fast shutter (1/1000) = less light + frozen motion.
And here's the fundamental difference between stills and video: in video you don't have free choice of shutter speed, because it's tied to frame rate.
The 180-degree shutter rule
The practical rule: set shutter speed to double your frame rate.
| Frame rate | Matching shutter speed |
|---|---|
| 24 fps | 1/50 |
| 25 fps | 1/50 |
| 30 fps | 1/60 |
| 60 fps | 1/120 |
The reason is that this produces the amount of motion blur the eye has grown used to in cinema. Push the shutter much faster and motion looks choppy and unpleasantly sharp; drop it much lower and it smears.
The practical consequence: in video you're left with two sides for controlling exposure — aperture and ISO — plus a third tool we'll come to shortly.
Side three: ISO
ISO is how strongly the sensor responds to light.
- Low ISO (100) = clean image, but needs plenty of light.
- High ISO (6400) = brighter image in low light, but with noise appearing as coloured grain.
Base ISO is the value at which the camera produces its cleanest image, often 100 or 200. Some cameras have two base values (dual native ISO), the second higher and usable in low light without heavy noise.
The rule: raise ISO last, after you've exhausted aperture and lighting.
The fourth tool: the ND filter
Shooting outdoors in daylight presents the opposite problem: too much light. You can't raise shutter speed because the 180-degree rule forbids it, and you can't drop ISO below base.
The answer is a neutral density filter — darkened glass placed in front of the lens that cuts light without shifting colour. Think of it as sunglasses for the camera, and it's among the most neglected accessories despite its large effect.
Other essential terms
White balance. Setting the camera to the colour of the light in the room, measured in Kelvin. Daylight is around 5600K, indoor tungsten around 3200K. Getting it wrong leaves the image excessively blue or orange.
Frame rate. How many images are recorded per second. 24 or 25 for a cinematic look, 50 or 60 when you want to slow motion down in the edit.
Dynamic range. The camera's ability to hold detail in both the very bright and very dark areas of the same shot.
Histogram. A graph showing the distribution of brightness in the image. More reliable than judging by eye on a screen, particularly in sunlight.
Focus. Sharpness on the subject. Manual focus is safer than autofocus for static shots, because autofocus can hunt mid-take.
Prime and zoom lenses. A prime has one focal length, usually a wider maximum aperture and a cleaner image; a zoom is more flexible.
The order to set things in the field
Follow this order every time:
- Frame rate according to the shot type (normal or slow motion).
- Shutter speed = double the frame rate, then don't touch it.
- White balance according to the light source, set manually rather than automatically so it doesn't shift mid-take.
- Aperture according to the depth of field you want.
- ND filter if there's excess light outdoors.
- ISO last, and as low as possible.
This applies to phones too
None of the above is exclusive to professional cameras. Most professional camera apps on phones allow manual control of shutter speed, ISO, and white balance, and some phones accept clip-on ND filters.
The difference is that a phone has a smaller sensor and usually a fixed aperture, so you lean more on lighting and ISO. What a phone can and can't do is covered in Can You Create Content With Just a Phone?
The exercise that makes it stick
Film the same scene three times: once with a wide aperture, once at high ISO, and once with a shutter speed that breaks the rule. Then watch all three in sequence.
Reading an explanation gives you information; seeing the difference with your own eyes in a scene you know gives you an instinct you'll use in the field without thinking.