When you inspect a photo's EXIF data, three numbers do most of the storytelling: aperture, shutter speed and ISO. Together they form the exposure triangle — the three controls that determine how bright a photo is and how it looks. Understanding them turns a wall of metadata into a lesson you can learn from.
Aperture (the f-number)
Aperture is the size of the opening that lets light into the lens, written as an f-number such asf/1.8 or f/11. The counter-intuitive part: a smaller f-number means a larger opening and more light. Aperture also controls depth of field — how much of the scene is in focus.
- f/1.4–f/2.8: lots of light, shallow focus — a blurred background behind a sharp subject. Great for portraits.
- f/8–f/16: less light, deep focus — most of the scene sharp. Great for landscapes.
In EXIF this appears as FNumber or ApertureValue. See a portrait you love with a beautifully soft background? Check the f-number — it was probably wide open.
Shutter speed
Shutter speed is how long the sensor is exposed to light, measured in seconds or fractions of a second, like 1/1000 or 1/30. It governs motion: fast speeds freeze action, slow speeds create blur.
- 1/500 and faster: freezes sports, wildlife and children.
- 1/60–1/125: everyday handheld shots.
- Slower than 1/30: risks blur handheld, but can be used deliberately for silky water or light trails, usually on a tripod.
In EXIF this is ExposureTime or ShutterSpeedValue. A blurry photo with a slow shutter speed in its metadata tells you exactly what went wrong.
ISO
ISO is the sensor's sensitivity to light. Low ISO (100–200) gives the cleanest image; high ISO (3200 and up) lets you shoot in the dark but introduces grain, or “noise.”
- ISO 100–400: bright daylight, maximum quality.
- ISO 800–1600: indoors and shade.
- ISO 3200+: low light and night, at the cost of some grain.
In EXIF this appears as ISOSpeedRatings or PhotographicSensitivity.
How the three work together
The exposure triangle is a balancing act: change one and you usually compensate with another. Open the aperture and you can use a faster shutter or lower ISO. Reading a set of your own photos side by side — noticing which combinations produced the results you liked — is more instructive than any textbook, and the numbers are already sitting in your files.
Other useful EXIF settings
- Focal length (
FocalLength) — how zoomed-in the shot is, in millimeters. - Exposure compensation — whether you brightened or darkened from the meter's reading.
- Flash — whether the flash fired.
- Metering mode — how the camera measured the light.
Read your own settings
Upload one of your photos to MetaLens and look at the exposure fields. Compare a shot that worked with one that did not, and the metadata becomes a feedback loop for improving. For a reference to every field name you encounter, see the EXIF tag glossary.