photography basics


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.

Shutter Speed

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

Low light

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.

Motion blur

ISO lowest possible; Shutter speed auto (will be lower, creating blur); Aperture Priority with a higher aperture. Turn on ND (neutral density) filter.

Background blur (bokeh)

Aperture priority with a higher aperture to increase depth of field. Stand close to subject, background will be blurry. Turn on ND (neutral density) filter.

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