Light Controls in Photography
How Photography Works
Light Controls
 Photography is dependent on 3 major factors:
 Aperture / Fstop
 Shutter speed / Exposure
 Film or Paper Speed
Light Controls in
Cameras &
Enlargers
You’ll notice that both cameras
and the enlargers in the
darkroom have these light
controls. So, let’s define and
explain their functions:
Understanding
Aperture &
Exposure Time
Both cameras and enlargers have a lens where
light passes through to expose images.
The size of the hole where light passes
through can also be controlled, and this is
called the aperture.
They also have a control that determines the
amount of time light is exposed to the
photographic film or paper for. This is called
shutter speed or exposure time.
Aperture
 Aperture or Fstop- is the size
of the opening that lets light in
or out. We can equate it to the
pupil of your eye and how wide
or small your pupil is when it
adjusts to different lighting
situations. It controls light by
how big or small the opening
is—a large opening allows a lot
of light; a small opening only
allows a little light.
 Each unit is called a ‘stop’,
hence the term Fstop. You can
stop up or stop down by
changing the Fstop on your
camera or enlarger, ie.
changing from F5.6 to F4 and
vice versa.
Aperture is measured by a specific set of numbers, called ‘stops’:
1.8
largest
2.8
4
5.6
8
11
16
22
32
smallest
Depth of Field
 Aperture / Fstop also has a secret-identity— it
affects depth of field.
 If you pretend that what you are looking at
when you look out into the world is several
planes of glass all sandwiched together, you
can think of depth of field as how many planes
of field are in focus at any one time.
 The larger the aperture (the smaller the
number), the smaller the depth of field—
meaning only 1 or 2 planes of glass will be in
focus at that Fstop.
 The smaller the aperture (the larger the
number), the larger the depth of field—
meaning a larger depth and area will be in
focus as you focus on your subject.
Shutter Speed or
Exposure Time
Shutter Speed or Exposure Timeis how long the film or paper is
being exposed to light for.
In terms of our relating this to the
human eye, it is like blinking your
eye—it’s how long you open your
eyelids for.
It controls how much light is let in
by length of time—the longer the
amount of time, the more light is
allowed on the exposure.
Shutter Speed / Exposure Time
 Shutter speed on cameras is measured in fractions of seconds:
2
4
longest
8
15
30
60
125
250
500
1000
shortest
 We cannot hand-hold any exposure longer than 1/60 without using
a tripod; however, because our breathing and heartbeat will move
the camera.
 Pinhole camera exposures and darkroom exposures are measured
in whole seconds, not fractions
Motion & Blur with
Shutter Speed
 Shutter speed also has a secret-identity—
it affects motion or blur.
 The slower your shutter speed, the more
blur (or tracers) you can create in your
photograph.
 The faster your shutter speed allows you
to freeze and capture motion, such as a
speeding racecar.
 This effect also explains why we must use
tripods to capture a clear photo below
1/60, because we cause the blur at that
slow of speed just by breathing and being
alive.
Shutter Speed and Fstop act inversely upon each other:
F
t 2
2.8
4
4
5.6
8
8
15
11
30
16
60
22
125
250
Basically, each of their setting are measured in ‘stops’, so if you adjust the Fstop by 2 stops,
you have to re-adjust the shutter speed by 2 stops in order for the exposure to stay the
same.
The reason for this is that if you adjust the size of the hole (the aperture) that lets in light,
and you let in more light, then you will have to change the length of time that hole is open
for, the exposure time, because they both affect how much light hits your film or paper.
A good rule of thumb for making sure your exposure stays the same while you change
things like your depth of field, or adjust the shutter to avoid blur is:
Speed up, stop down;
Stop up, slow down.
Film & Paper Speed
Film and Paper Speed- refers to how quickly the film or paper absorbs light. It
is called the ISO or ASA of the paper or film. These numbers are logical and
progress in speed/absorption as they get larger. The bigger the number, the
faster the film reacts to light.
The common range of film ASA or ISO are:
100
200
400
800
(1600
Photo-paper has an ISO of about 10.
3200)
Grain Quality
The other difference between
film speed is the grain quality—
the lower the speed, the finer
the grain of the film and final
image. This is why portraits are
usually shot on 100-speed film.
Speed of film is also important in
capturing images in low-light
situations or of quickly-moving
subjects.
The Difference in Grain Quality
in different ISO films
Review of Light Controls
LIGHT CONTROL
Fstop / Aperture
DESCRIPTION
The size of the hole
that lets light in.
WHAT IT AFFECTS
Affects the depth of
field of an imagehow many planes of
focus will be in focus.
BENEFITS
Can control light by
size of hole. Can
determine how much
detail you want in
focus.
Shutter Speed /
Exposure Time
The length of time the
light sensitive material,
film or paper, is
exposed for.
Affects the capture of
motion or blurriness
of picture. Allows for
longer exposures in
low-light situations.
Can allow for nighttime photography or
artistic blur or sharp
capture in creative
photography.
Film or Paper Speed
How quickly a lightsensitive material can
absorb light and
respond to light.
It affects the grain
quality and can affect
the look of sharpness
of a print.
Allows for fine grain
film to shoot for good
skin quality. Film
speed can be
matched to speed of
photographic subject,
such as race cars, etc.