2. Understanding Exposure
Exposure. Defined
Some scenes are brighter than others
so the camera needs to control how
much light reaches the film/chip
Too little light – the image will be too
dark
Too much light – appears washed out
3. Understanding Exposure
Controlling Exposure
Two ways to control exposure in exact,
measured amounts are via the aperture and
shutter speeds
The aperture controls how much light enters
the lens and the shutter speed controls the
length of time the light strikes the film
4. Understanding Exposure
Controlling Exposure
Photographers use the terms stopping
down and opening up to describe what
happens when they change the amount of
light reaching the film.
Decreasing the exposure is to “stop down”
while an increase in exposure would be to
“open up”
5. Understanding Exposure
Apertures
The aperture is the bladed diaphram inside
the lens that opens or closes to control the
amount of light entering the camera.
f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16,
f,22, f/32, f/45, f/64
An f-stop refers to the size of the aperture.
The higher the number, the smaller the
opening. This is because all f-stop numbers
are actually fractions so an f-stop of f/2 can
be thought of as 1/2 of fully open and an f-
stop of f/8 is 1/8th the opening diameter
6. Understanding Exposure
Aperture cont…
Apertures have been standardized so that each
stop either doubles or halves the amount of light
reaching the film
An f-stop of f/2 lets more light in than f/8
7. Understanding Exposure
Apertures cont…depth of field
As the aperture is stopped down and gets smaller,
more of the background and foreground in the
scene becomes sharp. The area of acceptable
sharpness in a scene is known as the depth of
field.
8. Understanding Exposure
Apertures cont…
Wide apertures
Throw backgrounds out of focus
Essential in low light situations
Also known as fast apertures
Maximum apertures vary between lenses and
not all lenses have the same apertures
available
9. Understanding Exposure
Apertures cont…
Mid-Range Apertures
• Tend to give the highest resolution
pictures
Small Apertures
• Essential in very bright conditions
• When increased depth of field is desired
• Small apertures have large f/numbers
10. Understanding Exposure
Shutter Speeds
The shutter of a camera can be thought of as a
door that opens and closes extremely quickly.
It is actually closer to a curtain, but the
principle is the same.
How long the curtain remains open is the
shutter speed.
11. Understanding Exposures
Shutter Speeds cont…
Like apertures, the shutter speeds have been
standardized and each successive change in
the shutter speed is equal.
If you move up the scale such as from 1/4
sec to 1/8 sec or from 1/125 sec to 1/250
sec, you double the speed and half the light
transmitted (stopping down).
Conversely if you move from 1/60 sec to 1/30
sec (open up) you half the speed and double
the amount of light
12. Understanding Exposure
Remember the same having/doubling
principle is at work with apertures. If you
switch from f/8 to f/11, you will have “stopped
down” one stop allowing only half the light to
reach the film plain
What exists is a series of equal steps of
change in the amount of light reaching the
film by either the shutter speed or aperture
14. Understanding Exposure
Camera Shake
Camera shake occurs when too slow a shutter
speed has been selected for handholding
capabilities. The image becomes blurred and
sharpness is lost.
A general rule is to select a shutter speed at
least equal to the focal length you are using.
A 50mm focal length would require a shutter speed of 1/60 sec
to avoid camera shake
A focal length of 200mm would require 1/250 sec shutter
speed
