For quick search, select one of the following topics:
Proper Exposure Sunny Sixteen Rule Reciprocal Exposures 1/stop Difference Reciprocity Failure
Depth of Field Great Depth of Field Shallow Depth of Field Selective Focus
Images of Motion Stopped Action Blurred Motion Shutter Speed "B" Panning Shots
I. Why the need for meter exposure readings?
A. The energy differences
between the darkest areas one can see into and the ares of
brightest
light (where one can still tell that one source of light is brighter
than another) is well
beyond the tonal range a film can record.
B. A meter is then necessary to find the best compromises to allow
maximum use of a film's
limited response to light energies.
C. The
goal of the metering technologies
is to give the photographer the exposure settings
which will record that area of the view analyzed by the meter to be
rendered on the film as
the middle tonality/color, or the "medium gray" when photographing in
black and white.
II. For the camera meterto determine proper exposure, it must have four pieces of information.
A. Light
intensityof the
light illuminating the subject
B. Film
speed or film
sensitivity
C. Shutter
speed or
exposure time
D.
Aperture or
Lens' setting for size of its opening
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III.
For a
given film,
there is a well defined amount of light energy needed to achieve
"Proper
Exposure."
A. The
amount of light required by a film to make an exposure (the film's
sensitivity to light) is denoted by the
ISO or ASAnumber
rating.
1. The higher the ISO number, more sensitive the film (film needs
less light to make an exposure).
a. The
ISO number is the "film speed."
b. ISO = International Standards Organization, ASA = American
Standards Association.
1) In Europe, films are rated either by ISO numbers, or the DIN
(German) numbering system.
B. Analogy: when pouring water into a glass, a certain amount of
water is needed to "fill" the glass.
"Proper exposure" is represented by a full glass.
1. When a film receives enough light, it makes a "proper
exposure".
2. The glass can be filled with water in different ways: quickly,
slowly, spoonful by spoonful (incrementally).
3. Films can be given proper exposure by different ways
too.
a. Quick burst of bright light, like a flash.
b. Long exposures to dim light.
c. Multiple exposures of low light (increments), etc.
IV. The duration of time that films are exposed to light is control bycamera's shutter. Top of page.
A. Duration of time is incremental, set by the
"shutter's
speed."
1. Usual increments are based on fractions of a second
a. 1 second, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500,
1/1000, and so on.
b. Likewise, speeds greater than a second are 1 sec., 2 sec., 4 sec.,
8 sec.,etc.
B. Each increment is either 2x or 1/2 the amount between successive
steps.
C. On some cameras there will be shutter speed labeled "B." The name is a historic label referring to flash "bulbs." It differs from all other shutter speeds in that it is totally manual. The time the shutter is open is as long as the shutter release button is depressed. Therefore, the length of time the shutter is open is determined by the photographer.It is used to make very long exposures from a few seconds to a few hours. For best results, the shutter release button is activated with a cable release.
V. Lens opening is called the lens' aperture. Top of page.
A. Opening controlled by the lens' "diaphragm", a set of metal blades
inside the lens.
Size of opening is selected with the"f/stop"
ring.
B. f/stopsare
a mathematical relationship of the focal length of a lens and the
size of the
lens opening or aperture.
1. Thus actual numbers are independent of any particular
lens.
a. f/stop defined as focal length (in millimeters or mm) of lens
divided by diameter of
lens opening (again in mm).
b. Focal
lengthis
defined as the distance between optical center of lens and
the
position of the focused image of a subject at an infinite
distance.
1) Most focal lengths expressed in millimeters (mm).
2) Example: for the 50mm lens found on most 35mm cameras, when lens
is focused on a
star, the distance between lens' center and the film will be 50
mm.
a) A 50 mm lens set at f/2 means the lens opening is 25 mm in
diameter.
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C. The actual sequence of f/stop numbers is not standardized, but
most start at f/1.0.
1. The sequence used most often is set up so each
increment
between sequential f/stops is
either two times (2X) or one-half (1/2) the size of the next
f/stop.
2. f/stop sequence:
f/1 f/1.4 f/2 f/2.8
f/4 f/5.6 f/8 f/11
f/16 f/22
a. The size of the lens opening decreases
with each larger f/stop number.
1.) Examples:
f/2 is 2x as large as f/2.8
f/8 is 2x as large as f/11
f/2 is 1/2x as large as f/1.4
f/8 is 1/2x as large as f/5.6
D. Theincrementbetween
the each whole step of f/stops is
called"1/stop"
1. Using the glass of water analogy, f/stops could represent the size
of a funnel used to
pour water into glass.
a. A funnel with opening of "size f/2" would allow twice the amount
of water
to flow, as a funnel of "size f/2.8"
b. If glass took 1 second to fill with "f/2 funnel", it would then
take 2 seconds to
fill with "f/2.8 funnel"
2.
So to get "proper" exposure, there is a certain time required for
each f/stop.
VI. 1/stop
Difference in
exposure: from a given initial exposure setting,
any
change in settings Top
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which is a change of 1/2X or 2X as much exposure.
A. Changing shutter speed one increment is a 1/stop change.
Example: changing from 1/30 sec.
to 1/60 sec. (1/2X), or changing 1/500 sec. to 1/250 sec. (2X) are
both 1/stop changes.
B. Changing f/stops one increment is a 1/stop change. Example:
changing f/4 to f/5.6 (1/2X),
or f/11 to f/8 (2X) are both 1/stop changes.
VII.Proper
exposureis then
choosing a combination of f/stops and shutter speeds to get
enough Top
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light to make the desired exposure.
A. Too much light (like overfilling the glass of water) will cause
too
much exposure
= overexposure
B. Too little light (not enough to fill glass) will cause
too
little exposure =
underexposure
or incomplete image development.
VIII. "Sunny Sixteen Rule:" a generalized exposure calculation for taking pictures outdoors Top of page.
A.
Rule applies only for pictures taken at mid-day (10AM - 3PM) for
subjects in direct sunlight.
Exposure directions as follows:
1. Must have film speed number (ISO #). Example:
for Ektachrome 100+: ISO rating is 100.
2. Shutter
speed will be at 1 / (ISO #).
Thus for ISO 100, shutter speed is 1/100 sec.
a. For practical purposes, use the nearest shutter speed
available;
for most cameras a speed of 1/125 is used for 1/100, 1/250 for IS0
200, 1/60 for IS0ÿ 64, etc.
3.
The lens is set at f/16.
4. It's possible to estimate exposures for subjects in shade, usually
2/stop more exposureÿ needed.
These "rules" were often used prior to availability of built-in light
meters.
IX.Reciprocal
exposures are
combinations of different shutter speeds and f/stops giving the
same Top
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exposure to the film
A. Reciprocal
exposures = equivalent exposures
B. Calculating reciprocal exposures
1. Recall f/stops are in increments of 2x or 1/2x for each 1/stop
difference
2. Shutter speeds are also spaced out in 2x or 1/2x increments or in
"1/stop" increments.
3. So a change in one value of f/stops requires an opposite change in
shutter speed to maintain
equivalent exposures.
a. Examples:
1). Start with exposure at f/8 at 1/125.
If
lens aperture is change f/8 to f/11, change is 1/stop less
exposure.
So a change in shutter speed is needed to compensate.
Then shutter speed is changed to 1/60, to give 1/stop more
exposure by time.
The
result is an equivalent exposure.
2). Again, start with exposure at f/8 at 1/125.
If change 1/125 to 1/250, change is 1/stop less exposure. Change
f/stop to
compensate: change f/8 to f/5.6 for a 1/stop increase in light
passing through
the lens. Result is an equivalent exposure with a different set of
lens
aperture and shutter speed.
C. Films have a defect called
reciprocity failure.
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1. When shutters speeds are shorter than 1/1000th second or longer
than one second,
equivalent exposures do not work. Film speed appears to slow down,
resulting in underexposure.
I. Lens aperture controls Depth of Field (d.o.f.) Top of page.
A. Depth of field is the range of distances from the camera in which
the image appears to be in-focus.
Actually, in a photograph, the only subject truly in-focus is the
subject the camera's lens was focused on.
Everything else is in various degrees of out-of-focus. The further
away something is in distance in front
of or behind the subject focused on, the more it will appear to be
out-of-focus.
B. A
large range of distances which appears in-focus is
a great
depth of field.
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This is achieved with the lens
aperture at f/11, f/16, f/22, etc. These
are the smallest lens apertures
or lens openings.
1. The most extreme great d.o.f. is achieved with a "pin-hole" camera. This is a camera with an aperture the size of a hole made with a needle. In the picture, everything is of equal focus sharpness. Actually, everything is equally "fuzzy" as nothing is truly in-focus, everything is in soft-focus. Therefore, the use of very small aperture like f/32 or f/45 with a lens designed for 35mm cameras will often make images that are less sharp than images taken at f/11 or f/16.(Click to see examples. )
C.
A very limited range of distances which appear in-focus is
ashallow
depth of field.
This is achieved with a
lens aperture at f/4, f/2.8, f/2,
etc. These are
the largest lens openings.
1. The
use of a limited depth of field to isolate your subject from the rest
of the image is
called Selective
Focus.
This is a picture in which the subject you focused on will be the
only
thing in-focus. Everything in front of or behind the subject will be
out-of-focus.(Click
to see examples. )
II.Selection of shutter speed for depiction of motionin a still photograph. Top of page.
A. The selection of shutter speed is used to show something is in
motion. There are three
types of "motion" pictures:
1. Freeze
frame or Stop Action.
The subject that is in motion is frozen in time, or stopped in
mid-action.
This is commonly used in pictures of sports action, dancers( animals
running or flying,
to freeze a stream of water, to catch any scene that's "quicker than
the eye."
a. Must
use a shutter speed faster than 1/500th of a second:
1/500, 1/1000, 1/2000, the
shorter the better.
(Click to see
example)
b. Note:Most
electronic flashes produce burst of light which are very short in
time.
Typically, flashes last around 1/400th to 1/800th
second.
Hence,
flash pictures qualify as "stop action"
pictures.
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2.Blurred
motion.
In these pictures, @I<only
the subject> is blurred;
as opposed to having the
entire picture blurred. Therefore, the subject is blurred but
everything else in the picture is clear.
a. Use
a slow shutter speed, like 1/15, 1/8, 1/4, 1/2
second. Be sure
to support or brace the camera
for these long exposure times, otherwise you will experience camera
shake
and the whole picture will be blurry. (Click
to see examples
)
b. To record light streaks made by moving lights, like auto head and tail lights, requires the use of very long shutter speeds. To achieve exposures of several seconds to several minutes, use the special shutter speed of "B." Not all cameras provide this option. Many automatic cameras will make exposures as long as 30 second or more. Usually, the lens is set at the smallest aperture, like f/22, f/32, f/45, etc. Bracket the exposures as most metering systems do not function when the camare is set on "B."(Click to see example )
3. Panning
pictures.
A special type
of blurred image in which the subject is in relatively
good focus and the background is streaked. The
streaked
background is
the key feature
of this technique, as it is what makes the image "move". If the
background is just blurred
or out-of-focus, the image might be just a shallow depth-of-field
picture.
a. Use
a slow shutter speed like a blurred motion
picture: 1/30,
1/15, 1/8, 1/4, etc.
However, to have the subject in-focus, you must move the camera to
follow the subject
as it moves across your field of view. The degree to which you are
able to follow the subject,
in the final picture. The hard part is to take the picture as you
follow the subject.
You must not stop following the subject as you take the
picture.
This is difficult with many cameras as the viewfinder goes dark when
you take the picture.
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page.
The following instructions
are procedures for altering the exposures used in making your
photograph. The "normal" exposures are the usual camera settings
based upon the camera's meter system responses to lighting and other
variables of picture taking. Bracketing
means to intentionally change the exposure to get lighter or darker
than normal images.
I. Overexposure,
to make the image lighter than
normal:
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Bracketing for 1/stop MORE exposure: Using the camera's meter "normal" reading as a starting point, either decrease the shutter speed one step (like 1/125 to 1/60) or open the lens aperture one increment more. Remember, the numbers for f/stops on the lens go backward. So to open the lens one stop would meanÿmoving the aperture control to the next lower number (like changing f/8 to f/5.6).When changing shutter speeds, remember to pay attention to problems of using speed below 1/60th second. It's always wise to find some type of support to brace yourself or your camera to avoid "camera shake" during slower exposure times.
(Click to see example)
II.Underexposure, to make the image darker than normal: Top of page.
Bracketing for 1/stop LESS exposure: Using the camera's "normal" meter reading as a starting point, either increase shutter speed one step, or close down the lens aperture one increment (go to the next higher number setting). In many situations, such as in dramatic lighting conditions, it is often advantageous to bracket the normal exposure with even greater variation than 1/stop less. Try 2/stops and 3/stops less exposures than the than normal exposure.(Click to see example) For extremely dramatic sunset images, it is not unusual to try exposures that are 4/stops or even -5/stops darker than normal. Naturally the landscape will be very dark, even black out, but the sun and the surrounding sky will be more colorful.
Important:
When "bracketing" exposures, just
change one control:
either the shutter speed or lens aperture.
Changing
both could get very confusing.
If your camera has
automatic exposure controls, manually changing the exposures will
usually
make the camera signal an
error in exposure. Disregard the signals, and just shoot at the
manual settings.
If you have an automatic
camera with built-in bracketing adjustments, making bracketed
exposures
is greatly simp lified. The
"normal" setting for exposure compensation is most often indicated as
"0", "1X", or "off".
To bracket, you are to set
the exposure control to "2X" or "+1" to make a 1/stop lighter
picture.
Similarly, set the control
to "1/2X" or "-1" to make a 1/stop darker picture.
If in doubt, consult your
camera's operations manual.
Again, always check which shutter speeds you are using, to remind yourself to take precautions against possible camera shake.