Aperture, shutter speed and ISO are the three settings that control how bright a photo is, and each one also changes the look of the picture. Aperture shapes depth of field, shutter speed shapes motion, and ISO shapes noise, so changing one usually means adjusting another to keep the same exposure.
Aperture: How Much Light Enters
Aperture is the opening in the lens, written as an f-number such as f/2, f/5.6 or f/11. A smaller number means a wider opening, more light and a shallower zone of sharpness. A larger number means a narrower opening, less light and more of the scene in focus.
- Wide (f/1.8 to f/2.8): portraits, dim rooms, blurred backgrounds.
- Middle (f/4 to f/8): everyday shooting, usually sharp across the frame.
- Narrow (f/11 and above): landscapes where foreground and distance should both look sharp.
Shutter Speed: How Long the Sensor Sees
Shutter speed is the length of time the sensor collects light, written as fractions of a second. Fast speeds freeze movement and slow speeds let it blur.
- Roughly 1/500 and faster freezes most walking, running and sports action.
- Around 1/125 suits casual people shots.
- For handheld shots without stabilization, a common guide is a speed near one over the focal length, such as 1/50 for a 50mm lens.
- Slow speeds of a second or longer need a tripod and suit night scenes and flowing water.
ISO: Sensor Sensitivity
ISO amplifies the signal from the sensor. Low values such as 100 or 200 give cleaner images in bright light. Higher values let you shoot in dim places but add visible grain, called noise. How much noise you accept depends on your camera and how large you plan to print or display the image.
Putting the Three Together
- Decide what matters most: blur, motion or low noise.
- Set that control first. For portraits, set a wide aperture. For action, set a fast shutter speed.
- Set ISO as low as the light allows.
- Check the exposure on the screen or histogram.
- If the image is too dark, open the aperture, slow the shutter or raise the ISO, one step at a time.
| Scene | Aperture | Shutter | ISO |
|---|---|---|---|
| Bright outdoor portrait | f/2.8 | 1/500 | 100 |
| Landscape on tripod | f/11 | 1/10 or slower | 100 |
| Indoor family photo | f/2.8 | 1/125 | 800 to 3200 |
These values are general guidance, not rules. Real light varies, so adjust to what you see.
FAQ
Which setting should a beginner learn first?
Aperture, because the blurred background is the most visible change. Try aperture priority mode and let the camera handle the rest while you learn.
What is a stop?
A stop is a doubling or halving of light. Each full change in aperture, shutter speed or ISO moves exposure by one stop.
The Short Version
Aperture controls depth, shutter speed controls motion and ISO controls noise. Choose your priority, keep ISO low, and balance the others. Practice on one subject until the trade-offs feel natural.
