Photography help - Simple tips to control exposure

CONTROLLING EXPOSURE

In order for an image to be captured on film it must be exposed to light.  The camera had two settings to control light and they work very similar to the human eye.

The Shutter

The shutter blocks all from exposing the film until you press the button, then it quickly opens and closes giving the film a brief flash of light

Shutter Speed

To control the amount of time the shutter stays open

Longer shutter speed = more light

Shorter shutter speed = less light

Amount of time the sensor is exposed to light

Used to freeze or blur subjects

Shutter speed examples:

A half second exposure is ONE STOP darker than a one second exposure

A 1/125 exposure is TWO STOPS brighter than a 1/500 exposure

A 1/1000 exposure is THREE STOPS darker than a 1/125 exposure

THE APERTURE

Before light reaches film it must pass through an opening called an “aperture”.  The aperture is like a pupil, you can control the aperture by setting the “Aperture Opening” known as an F-Stop.

Smaller F-stops numbers = larger openings = more light

Larger F-stops = smaller opening = less light

The Size of the opening that lets light into the camera

Controls the depth of field what is in focus and what isn’t

• Blurred background = wide aperture = low f-stop
• Everything in focus = narrow aperture = high f-stop

Like the pupil in a human eye the aperture on a camera controls light, it does so by closing up to restrict light and opening to let it through.

Aperture Settings (F-Stops):

moving from f16 to f8 is:

TWO STOPS brighter

moving from f5.6 to f8 is:

ONE STOP darker

Moving from f4 to f2.8 is:

ONE STOP brighter

BALACING SHUTTER AND APERTURE

Exposure is about different combinations of shutter speed and f-stop settings.  These combinations can drastically affect the finished picture.

Take a stop, give a stop:

Since f-stop and shutter are both measured in stops keeping the balance is easy, if you take away 2 stops from the aperture you can give two stops back with the shutter and end up with the same exposure level.

AN EXAPMLE

If you are photographing a parade and your light meter indicates a proper exposure of 1/125 at f11.  But, you want to use a faster shutter speed to freeze the action of those marching past and decide that 1/250 would be more appropriate.

Changing from one shutter speed to another which is twice as fast (1/125 to 1/250) allows half as much light to strike the film and therefore your picture would be underexposed, but if you open up the aperture by one stop it will allow twice as much light to come in and you will have proper exposure again.

The faster shutter speed reduced the light striking the film by 50% but changing to a wider aperture compensate for this reduction by doubling the amount of light, thereby preserving the proper exposure.

In this example both 1/125 at f11 and 1/250 at f8 will give proper exposure but the exposure with faster shutter speed as more action-stopping ability.

TIPS

A brightly lit scene can be correctly photographed by closing the aperture and using a faster shutter speed

When you come inside to a dark place after being in a bright place your iris opens out and vice versa, a camera needs to do the same… the aperture being the iris

Remember that shutter speed, f-stop settings and even film speed are all rated in units of “stops”

If you decrease a stop in shutter speed you must add a stop in aperture and vice versa

1/125  f5.6  ISO 100 is as bright as:

1/250  f4  ISO 100 is as bright as:

1/500  f4  ISO 200