Exposure is how much light reaches the sensor. Three settings control it, and any of them can brighten an image — so the real skill is choosing *which* one to change, because each has a distinct visual side effect.

Aperture: Controls Depth of Field

The aperture is the opening in the lens, measured in f-numbers. Confusingly, smaller number = bigger opening = more light.

  • f/1.8 — lots of light, shallow depth of field: a thin slice is sharp, the background blurs. Portraits, low light.
  • f/8 — moderate light, most of the scene sharp. The general-purpose choice.
  • f/16 — little light, deep depth of field: everything from near to far is sharp. Landscapes.

Side effect to remember: aperture decides how much of the scene is in focus. That's usually the most creatively important of the three.

Shutter Speed: Controls Motion

How long the sensor is exposed, in seconds or fractions.

  • 1/1000 s — freezes fast action: sport, splashing water, birds.
  • 1/125 s — general handheld shooting.
  • 1/30 s and slower — camera shake and subject blur become likely handheld; needs a tripod or stabilization.
  • 1 s or longer — deliberate motion blur: silky water, light trails.

Rule of thumb for handholding: shutter speed at least 1 / focal length (1/50 s for a 50 mm lens), faster if you've had coffee.

Side effect: shutter speed decides whether motion is frozen or blurred.

ISO: Amplification, Not Light

ISO doesn't collect more light — it amplifies the signal you already captured. That's why it's different in kind from the other two.

  • ISO 100–400 — clean, maximum detail. Use whenever there's enough light.
  • ISO 800–3200 — visible noise, fine for most uses on modern sensors.
  • ISO 6400+ — noticeable grain, reduced dynamic range and colour accuracy.

Side effect: noise and lost detail. Treat ISO as the setting you raise *last*, when aperture and shutter can't give you what you need.

They Trade Off in Stops

Each "stop" doubles or halves the light. Open the aperture one stop and you can halve the shutter time for the same exposure. This is the whole game: pick the setting that matters for the look you want, then trade the others to balance.

Choosing by Situation

  • Portrait — aperture first (wide, for background blur), then shutter fast enough to be sharp, then ISO to fill the gap.
  • Sport / kids / pets — shutter first (fast, to freeze), then open the aperture, then ISO.
  • Landscape on a tripod — aperture first (narrow, for front-to-back sharpness), ISO at base, shutter as long as needed.
  • Low light handheld — widest aperture, slowest shutter you can hold, then raise ISO to whatever it takes. A slightly noisy sharp photo beats a clean blurry one every time.

On Phones

Phone cameras choose all three automatically and rely heavily on computational processing, but the concepts still apply: pro/manual modes expose them directly, and even in auto mode, tapping to set exposure and understanding *why* a night shot is blurry (long shutter) or grainy (high ISO) tells you what to change — usually more light, or a steadier hold.