ISO Aperture Shutter Speed

Start with a Good Exposure

ISO, Aperture and Shutter Speed are the basis of exposure,

and the first thing to think about technically when taking a photograph.

You need enough light to hit the sensor (or film), but not too much.

Learning what these three variables are and how to control them is crucial to all kinds of photography.


ISO adjusts the level of sensitivity to light of your light sensor.

Like the film, the higher the ISO number, the less light is needed to achieve the correct exposure.

e.g. 100 ISO film was good for outdoors and 400 was good for indoors

50, 100, 200, 400, 800, 1600, 3200, 6400 (full stops, aka steps)


50 64 80 100 125 160 200 250 320 400 800 1600 (with 1/3 increments)

As ISO is increased in digital photography, noise often results in the darker tones (ie the shadow areas).

A higher ISO number may allow you to handhold the camera in a low light situation.

A lower ISO number will give less or no noise, but in low light, the situation may require a tripod.

F Stop / Aperture

The aperture ( also called f stop) is like the iris in our eye,

the wider it is open, the more light is allowed in.

f 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 are aperture settings in full stops (aka steps)

<—doubles with each full step<—<—- —->—>half as much light per full step—>

1, 1.1, 1.3, 1.4 1.6, 1.8, 2, 2.2, 2.5, 2.8 3.2, 3.6, 4, 4.5, 5.0, 5.6, 6.3, 7.1, 8, 9.0, 10.1, 11, 12.7, 14.3, 16, 18.0, 20.2, 22, 25.4, 28.5, 32

(f stop with 1/3 increments)

Each stop (aka step, i.e. a full unit of exposure) is half as much light as the numbers increase (f 4 lets in half as much light as f 2.8).

Each stop is twice as much light as you move from an aperture to the next lower aperture number (f 2.8 is twice as much light as f4).

Depth of field

Depth of field equals how much is in focus.

Aperture controls the depth of field, the wider the f stop opening, the smaller the depth of field in front of and behind your subject.

The larger the number the smaller the aperture, the more that is in focus in front of and behind your point of focus.

For example: with f 2.8 set, the eyes are sharp and the ears are out of focus.

The same shot at f 8 set, the eyes, ears, and wall behind are all in focus.

A wider aperture (e.g. f 2.8 or wider) can be a very useful hand-holding in a low light situation to obtain the correct exposure.

Lenses with a wide aperture (2.8 or wider) are called fast lenses.

A smaller aperture (e.g. f 16)can be useful for shooting a large area where you want things close and distant all in focus.

Shutter Speed

The shutter speed controls how long the shutter is open.

A typical range of shutter speeds might be:

1 second, 1/2second, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000

<—–more light-doubles <—– —–>less light-half—–>

…1,1/2, 1/2.5, 1/3.2, 1/4, 1/5.0, 1/6.4, 1/8, 1/10, 1/12, 1/15, 1/20, 1/25, 1/30, 1/40, 1/50, 1/60, 1/80, 1/100, 1/125, 1/160, 1/200, 1/250…

(shutter speed in 1/3 increments)

The shutter speed doubles as you move higher and halves as you move to lower numbers:

1/1000 is twice as fast as 1/500 and 1/500 will stay open twice as long as 1/1000

Too slow of a shutter speed can result in loss of sharpness due to camera or subject movement during exposure.

I’ve seen students handhold at shutter speeds of 1/4 of a second and get a sharp enough image.

exposure triangle diagram