A friend once asked me why anyone would shoot in Manual mode when a camera takes great pictures on Automatic. Fair question. My answer: in Manual, the camera is taking the picture I actually intended. This post is meant to introduce the basics of exposure in a way that’s easy to follow, not intimidating — not the full deep-dive, just enough vocabulary to get you started.
Exposure is just the amount of light that reaches your sensor. “Photography” literally means writing with light, so getting the right amount of it is the whole game. Three settings control that: Aperture, Shutter Speed, and ISO.
Aperture
The aperture is the physical opening in your lens that lets light through — think of it like the iris in your eye. Bigger opening, more light. It’s measured in f-stops (f/2.8, f/22, and so on) — a smaller number means a bigger opening and more light; a bigger number means a smaller opening and less light. Each full stop you open up doubles the light hitting the sensor.
Shutter Speed
Shutter speed is how long the sensor is exposed to that light. Same doubling logic applies — go from 1/500th to 1/1000th and you’ve cut the light in half; go from 1/500th to 1/250th and you’ve doubled it.
ISO
ISO is how sensitive your sensor is to light — higher ISO needs less light for a good exposure, lower ISO needs more.
A Simple Way to Picture It
Think of filling a glass at the kitchen sink. A full glass is your ideal exposure — the water is your light. A trickle from the faucet is like f/22: it takes a full minute to fill the glass. Open the faucet up (like opening your aperture to f/16) and the glass fills in half the time. ISO is like the size of the glass itself — a smaller glass (higher ISO) needs less water to fill.
Try It
Put your camera in Manual, take a shot of anything, and check the LCD. Too bright? Too dark? Adjust one of the three settings until it looks right. Then pick a different one of the three and adjust it to compensate, keeping the same exposure. Do this enough times around the house and it starts to feel automatic — which is really the whole point.