What Is ISO? — Simply Explained
ISO controls how sensitive your camera sensor is to light. Think of it as your camera's ability to see in the dark. A higher ISO makes the sensor more sensitive, letting you shoot in darker conditions — but there's a trade-off.
How Does ISO Work?
ISO is measured in numbers: 100, 200, 400, 800, 1600, 3200, and so on. Each doubling means twice the sensitivity to light. ISO 100 is the least sensitive (best for bright daylight), and higher values are for darker situations. The trade-off: higher ISO introduces grain or noise — that speckled, grainy look in photos. Modern cameras handle high ISO much better than older ones, but the principle remains.
When Should I Change ISO?
Keep ISO as low as possible for the cleanest image. In bright sunlight, use ISO 100–200. On cloudy days, try ISO 400. Indoors, you might need ISO 800–1600. At night without a tripod, ISO 3200 or higher may be necessary. The rule of thumb: only raise ISO when you can't get enough light through aperture and shutter speed alone.
Practice Tip
Try this: photograph the same subject at ISO 100, ISO 1600, and ISO 6400. Zoom in to 100% on your computer and compare the noise levels. This helps you understand your camera's ISO limit — the point where noise becomes distracting.
Frequently Asked Questions
Is ISO 100 always the best choice?
ISO 100 gives the cleanest image but only works in bright light. If your photo is too dark at ISO 100, you need a higher value. A sharp photo with some noise at ISO 1600 is better than a blurry one at ISO 100 with a shutter speed that's too slow.
What does Auto ISO do?
Auto ISO lets the camera choose the ISO value automatically while you control aperture and shutter speed. It's a great stepping stone between full Auto and full Manual mode. Most cameras let you set a maximum ISO so it won't go too high.
Put It Into Practice
Use the wizard to get camera settings for your next shot — based on what you just learned.