Elements of Light in photography

Elements of Light

UNDERSTANDING THE THREE ELEMENTS OF EXPOSURE

ISO. The light sensitivity of the film or digital

sensor.

Aperture. A moving diaphragm within the

lens that controls the amount of light passing

through the lens and into the camera. F-stops

are the numeric designations referring to the

size of the aperture.

Shutter. A mechanical device that opens and

closes very quickly, letting light into the camera

and in contact with the digital sensor (or

film). The length of time the shutter is open

is known as shutter speed.

ISO

ISO (International Organization for Standardization) is a body that sets international

and commercial standards. In digital photography, the ISO is the measure of the digital sensor’s

light sensitivity. Digital sensitivity correlates to film speed in traditional cameras. Digital cameras 

can have ISO settings from 50 through 3200. The standard ISO settings that you use most of the

time are 100, 200, and 400. A lower number and sensitivity, 50 to 200, requires more light and,

thus, is called slow, but an ISO that is larger, 400 to 1600, needs less light, can shoot the same

scene with a faster exposure, and is considered a faster ISO. 

With each 1 f-stop change higher in the ISO, you

effectively double the sensitivity of the film or

digital sensor. As you raise the ISO sensitivity

each stop, 100 to 200 to 400, the sensor becomes

more light-sensitive, and you need less light to

get your exposure.

The lower the number, the less light sensitive the

digital sensor is. Less light sensitivity means that

you need more light to achieve the correct exposure.

At the lower ISOs, 50 and 100, you achieve

the highest image quality in both film and digital.

THE APERTURE

The lens aperture is a moving diaphragm within the barrel of the lens; it determines how much

 light passes through the lens and into the camera.The designation for each step in the aperture is

called the f-stop. A smaller f-stop or f number means that the actual opening of the aperture is

larger, and the higher numbered f-stops designate smaller apertures, letting in less light. 

The f number is the ratio of focal length to effective aperture diameter. 

The relative size of the changing aperture and corresponding f-stops

THE SHUTTER

Stopping action or avoiding blurry subjects is generally a desired quality of a photograph. Choosing

an appropriate shutter speed greatly determines your success in achieving this. In most cases, a

camera’s shutter consists of small thin pieces of metal that move very quickly, opening and

closing. Two types of shutters exist, focal plane shutters and leaf shutters. A focal plane shutter is

found in most digital single lens reflex (DSLR) cameras and is located right in front of the digital

sensor, just behind the lens. The horizontal blades of the shutter rise and fall rapidly to expose 

the sensor to light. 

Your camera’s shutter opens and closes

just in front of the digital sensor, allowing light in

for only as much time as needed to create the

exposure. In digital point-and-shoot cameras, the

lens is built into the body of the camera, and the

shutter is built into the lens. These shutters are called leaf shutters,

and they work much like the

aperture in that the blades progressively dilate to

the circular opening of the lens.

Shutter speed is changed with a turn of the shutter

speed dial. This is different in many cameras:

With some, it is a dial turned by the forefinger;

on others the thumb wheel; and some cameras

enable you to select which dial is the shutter

speed dial.With each full change of the shutter

dial, the shutter is open for twice as much, or half

as much time. For example, if your camera is set

at ISO 100, the f-stop at f/11, and shutter to

1/125, and you want to stop the action, changing

the shutter to 1/250 reduces blurring, but it also

makes the image 1 stop darker. To maintain the

same exposure, you also have to change your fstop

to f/8 or change the ISO to 200. Shutter speeds can be faster than 1/10,000 of a

second or as slow as many hours, but in most realworld

photography, the shutter is open for just a

fraction of a second. For example, a standard daylight

exposure might be 1/125 of a second at f/11

using ISO 100. Using a faster shutter speed stops

motion, and a slower one can induce blur, and each has its place.