ISO adjusts the level of sensitivity to light of your light sensor. Like 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 hand hold the camera in a low light situation.
A lower ISO number will give less or no noise, but in a low light situation may require a tripod.
F Stop / Aperture
The aperture 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 steps (aka stops)
<—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
(ISO 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 let’s in half as much light as f 2.8).
Each stop is twice as much light as you move from an f stop to the next lower aperture number (f 2.8 is twice as much light as f4).
Depth of field
Depth of field = how much is in focus.
Aperture controls depth of field, the wider the f stop opening, the smaller the depth of field in front of and behind your point of focus
The smaller 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 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.
The shutter speed controls how long the shutter is open.
A typical range 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—–>
2 2.5, 3.2, 4 5.0, 6.4, 8 10, 12, 15 20, 25, 30 40, 50, 60 80, 100, 125 160, 200, 250 320, 400, 500 640, 800, 1000
(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
These 3 variables are universal with any camera, digital or film, and are the basis of exposure with every photograph. A correct exposure is when your image is not too light and not too dark. To maintain the same exposure of a given subject, if you change one of these 3 variable to allow for more light, you need to change one of the other 2 variables to let in less light. These variables have an inverse relationship, e.g. changing the f stop to to allow more light, then you need to change either the shutter speed or ISO to let in less light if you want to keep the same exposure.
Longer shutter speeds may be necessary for lower light situations, while higher speeds may be needed in brighter situations.
Slower shutter speeds can be harder to hand hold, causing lack of sharpness due to camera shake.
Faster shutter speeds can freeze action, but require more light and/or a higher ISO and/or a wider aperture.
Longer exposures of a second or more can also create noise patterns, especially in older digital cameras.
If your camera moves during a longer exposure, image quality may suffer from lack of sharpness due to camera shake. A tripod holds the camera steady at slower shutter speeds, allowing you to carefully frame your subject and freeing up your hands. A cable release can be an added tool to ensure the camera doesn’t move during exposure.