Aperture, shutter speed and ISO, and how the three work together to control both the brightness and the look of a photograph.
Learn Photography · Camera & exposure
Exposure is just a word for how bright or dark your photograph is. You control it with three settings, and because changing one affects the others, they are often drawn as a triangle. Learn how each one behaves and you can leave automatic mode behind for good.
The aperture is the opening inside the lens, written as an f-number like f/2.8 or f/11. It does two jobs at once. A wide opening (a low f-number such as f/2.8) lets in plenty of light and throws the background out of focus, which is why portraits often have that soft, creamy backdrop. A narrow opening (a high f-number such as f/11) lets in less light but keeps far more of the scene sharp, which is what you want for landscapes and larger groups.
So aperture controls brightness and depth of field, meaning how much of the photo is in focus, at the same time.
Shutter speed is how long the sensor is exposed to light, written as a fraction of a second such as 1/500 or 1/60. A fast shutter freezes movement, which is essential for children, pets and sport. A slow shutter lets movement blur, which can look beautiful for a waterfall but will also blur the whole photo if you are hand-holding and your hands move. As a guide, stay around 1/125 or faster when hand-holding, and use a tripod for anything slower.
ISO is how sensitive the sensor is to light. A low ISO like 100 gives the cleanest, sharpest image and is ideal in good light. Raising the ISO lets you keep shooting as the light drops, but it adds grain, known as noise. The habit to build is simple: keep ISO as low as the light allows, and only raise it when you have run out of room with aperture and shutter speed.
Because all three affect brightness, they trade off against each other. Picture a room getting darker. To keep the same brightness you could open the aperture wider, or slow the shutter down, or raise the ISO. Each choice has a side effect: a wider aperture softens the background, a slower shutter risks blur, and a higher ISO adds grain. Good exposure is choosing which trade-off suits the photograph in front of you.
A practical starting point for a portrait in soft daylight: aperture around f/2.8 to f/4, shutter around 1/250, and ISO as low as it will go while keeping that shutter speed. Adjust from there.
Once these feel familiar, try full manual mode for a day. It is the fastest way to make the triangle second nature.
For a broader start across composition, light and lenses, download our free beginner's guide, or head back to Learn Photography for more lessons.