By George Hsia, www.georgehsia.com
Together, ISO, Shutter Speed, and Aperture all play a part in letting light into the lens and getting a good exposure. Like filling a bucket, if you adjust one setting you must adjust another setting in the opposite direction so that you don’t get too much or too little water.
In this example if you open the faucet more it will take less time to fill the bucket as compared to opening the faucet just a little which means it will take longer to fill the bucket.
Likewise, if you want to decrease the shutter speed (longer time), you can either:
a) Change the size of the bucket, making it bigger
b) Change the aperture to decrease the amount of light, which means you need more time to fill the bucket.
c) You can change both ISO and aperture (a little of each), as long as you fill the bucket that’s all that matters.
Stop – A unit of measure to indicate half or double the amount of light. One stop more is 2x the amount of light. Two stops is 4x. One stop less is ½ and two stops less is ¼.
Because a stop can be measured for Aperture, Shutter Speed and ISO the photographer now knows how much to adjust other settings if one changes.
•f/2 allows double the amount of light as f/2.8 which means f/2 is one stop brighter than f/2.8.
•f/2.8 is one stop brighter than f/4 which is also one stop.
•f/2 allows four times as much light as f/4 which is two stops brighter than f/4.
Shutter Speed -
•1/30 allows double the amount of light as 1/60 which means 1/30 is one stop brighter than 1/60.
•1/60 allows double the amount of light as 1/125 which is also one stop.
•1/30 allows four times as much light as 1/125 which means it is two stops brighter than 1/125.
•ISO 100 requires double the amount of light as ISO 200 which means ISO 100 is one stop darker than ISO 200.
•ISO 200 requires double the amount of light as ISO 400 so it is one stop darker.
•ISO 100 requires four times more light as ISO 400 which means it is two stops darker than ISO 400.
Exposure Compensation – Because camera metering isn’t always accurate, the cameras gives the photographer the ability to adjust the exposure (brighter or darker) to suit the photographer’s preference. To brighten exposure, adjust exposure toward “+” and to darken exposure adjust exposure toward “-”. Most cameras can adjust in 1/3 stop increments up to three stops depending on the camera.