Aperture, shutter speed, ISO are all interrelated!
Changing one affects the other!

Exposure is like filling a bucket of water. Assume one gallon represents ‘proper’ exposure. You can get one gallon in the bucket very fast with a large hose (a large aperture like f2.8) turned on for a short time (a fast shutter speed). Or you can get a gallon of water with a very small hose (small aperture like f16) turned on for a longer time (slow shutter speed). Either way you end up with one gallon of water (proper exposure).

To maintain the same exposure:
– Changing to a larger aperture (lets in more light) needs a faster shutter speed (that lets in less light)
– Changing to a smaller aperture (lets in less light) needs a slower shutter speed (that lets in more light)

– Changing to a slower shutter speed (lets in more light) needs a smaller aperture (that lets in less light)
– Changing to a faster shutter speed (lets in less light) needs a larger aperture (that lets in more light)

It is very important to realize:
When camera is set to Auto or Program mode: when you change aperture or shutter speed the camera automatically compensates by changing the other a corresponding amount the opposite direction (to keep the exposure the same).

To make your photo darker or lighter you must increase or decrease exposure!
Increasing exposure causes the photo to be lighter (moves histogram towards the right)
Decreasing exposure causes the photo to be darker (moves histogram towards the left)
This can be accomplished in manual mode or by exposure compensation.

Using your camera in Manual mode: when you change aperture or shutter speed the other does not automatically change to compensate, therefore the image gets more or less exposure (making it darker or lighter).

You can also use exposure compensation. + gives more exposure, making the image lighter. Setting to – gives less exposure, making the image darker.



Aperture/f Stops
In 1 stop increments: f1.4, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45, f64, f128
In 1/3 stop increments: f5.6, f6.3, f7.1,f 8.0, f9, f10, f11, f13 etc.

Shutter Speeds
In 1 stop increments: I second, ½, ¼, 1/8th, 1/15th, 1/30th, 1/60th, 125th, 1/250th, etc.
One stop is always lets in twice as much light or half as much light.
In 1/3 stop increments: 1/30th, 1/40th, 1/50th, 1/60th, 1/80th, 1/100th, 1/125 etc.

ISO (film or digital sensor’s sensitivity to light)
In 1 stop increments: 100, 200, 400, 800, 1600, 3200, 6400.etc.
One stop always lets in twice as much light (lower ISO) or half as much light (higher ISO)
The higher the number the more sensitive to light the camera sensor becomes (but increases digital noise).


©Douglas Beasley 2014