The Golden Triangle: ISO, Shutter Speed, and Aperture
What it controls: Sensitivity to light.
How it is measured: Low ISO numbers are less sensitive to light than higher ISO numbers. 400 is twice as sensitive as 200, etc.
How to use it: Use a low ISO for bright light conditions, high ISO for dark conditions. Higher ISO allows faster shutter speeds or smaller aperture, but higher ISO introduces more noise.
What it controls: Amount of time the shutter remains open.
How it is measured: In fractions of a second (or seconds).
How to use it: Use slow shutter speed for low light (but can cause blur if the camera shakes or there is motion); fast shutter speed for motion.
What it controls: Size of hole in lens, lets more or less light through to the sensor.
How it is measured: Expressed in focal ratio to the lenth of the lens from the sensor. Inverse relationship: Low numbers mean wide opening, high numbers mean smaller opening
How to use it: Controls depth of field (sharpness of scene, or the part of the scene that is in focus). Small opening (higher f/ number) = larger depth of field; large opening = smaller depth of field. Wide aperture is ideal for darker conditions or no shadows;
narrow aperture for bright light or heavy shadows.
Interaction with Focus: Focus determines the focal point, depth of field determines how much in front and behind that point is clear.
Generally Useful Defaults
- Auto-Hi ISO, capped at 3200
- Use aperture priority to manually control depth of field (higher number = bigger depth of field - usually will want as high of an aperture setting as possible while having a fast enough shutter speed for the conditions). In aperture priority mode, camera automatically determines shutter speed based on the aperture you set, plus the available ISO.
- Aperture set to f/8 maximizes sharpness of lens.
- Use exposure compensation to quickly override automatic settings and adjust exposure on the fly.
- Rather than using flash, increase ISO. If that introduces too much noise into the photo, use a tripod and increase shutter speed.
Common Scenarios and Settings
ISO Auto-Hi; Shutter speed Auto (will be low); Aperture Priority (low number, to let in max light; will result in depth of field being shallow); May require tripod to avoid shaking; moving subjects will require flash to freeze movement.
If shake is a problem: Full manual - Increase ISO, open the aperture fully and make the shutter speed as fast as possible, Use 2-second timer to avoid camera shake.
ISO Auto; Shutter speed priority, high; Aperture low, depth of field may be shallow; Will require high light or flash to freeze motion.
ISO lowest possible; Shutter speed auto (will be lower, creating blur); Aperture Priority with a higher aperture. Turn on ND (neutral density) filter.