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THE CAMERA
CAMERA - A picture-taking device usually consisting of a light-tight
box, a film holder, a shutter to admit a measured quantity of light, and
a lens to focus the image.
The four types of cameras are categorized according to their viewing systems:
- View Camera - focusing image is seen directly
through the lens which will take the picture. Usually on a piece of
ground glass.
- Rangefinder/Viewfinder Cameras - focusing image
is seen through a simple lens "window" which shows an approximation
of the final picture view, but not the exact view.
- Single Lens Reflex - focusing image is reflected
from the actual taking lens by a mirror onto a piece of ground glass.
- Twin Lens Reflex - focusing image is reflected
onto a piece of ground glass from a focusing lens which is generally
situated directly above the taking lens - this focusing system encounters
the same problem as Rangefinder/Viewfinder Cameras in that the focused
image is an approximation of the final picture view.
SHUTTER - A mechanism that opens and closes
to admit light into a camera for a measured length of time.
- a shutter controls the amount of light to reach
the CCD or the film by how long it remains open
- each shutter setting is half (or double) the
time of the next one
- there are two major types of shutters:
- Focal-plane shutter - admits light to expose
film by moving a slit or opening in a roller blind just in front
of the film (focal) plane - generally faster shutter speeds are
available using this type of mechanism
- Leaf Shutter - admits light to expose film
by opening and shutting a circle of overlapping metal leaves
The shutter markings on an average
35mm SLR camera are:
B • 2 • 1 • 2 • 4 • 8 • 15 •
30 • 60 • 125 • 250 • 500 • 1000 •
2000
- B or Bulb keeps the shutter open as long as
the release button is held down.
- The numbers to the right of the B setting generally
denote seconds in decreasing order headed towards one. For instance
in the case above, the bold 2 and 1 mean 2 and 1 seconds respectively.
- Shutter settings which are less than one second
in length are listed next as ascending whole numbers. This may be misleading
however as these numbers actually denote fractions of seconds.
In this example the numbers
2 • 4 • 8 • 15 • 30 • 60 • 125 •
250 • 500 • 1000
actually denote times which are:
1/2 • 1/4 • 1/8 • 1/15 • 1/30 • 1/60 •
1/125 • 1/250 • 1/500 • 1/1000 of a second
SHUTTER AS CONTROLLER OF MOTION
- The shutter controls motion in a photograph
by how long it remains open.
- Generally speeds of 1/60 or 1/125 will stop
motion however if an object is moving quite quickly across the camera
frame faster speeds may be necessary.
- "Camera Shake" is a term used to describe
blur caused by camera movement during exposure. A camera can generally
be hand held without noticeable camera shake at 1/30 or 1/15 of a second.
- The amount of blur caused by a moving object
is not determined by how fast the object is moving, but instead by how
far it moves across the camera plane. For instance a speeding car photographed
from 10 feet away may be completely blurred at 1/125 of a second, while
from 500 feet away may show only the slightest signs of blurring. This
is because the car which is nearby passes across more of the film plane
than the car which is very far away.
In order to stop blur one can:
- shorten shutter speed (thus making it necessary
to increase aperture)
- pan which means to follow the moving object
with the camera (thus blurring the background while sharpening the moving
subject)
APERTURE - The size of the lens opening through
which light passes. (The "relative aperture" is measured as
the focal length of the lens divided by the diameter of the aperture)
- the aperture works like the pupil of an eye
shutting down in instances of bright light and opening up when there
is not much light
- Diaphragm - a ring of thin, overlapping metal
leaves located inside the lens which open or close to allow more or
less light through the lens.
Aperture settings are described as F-stops.
- the F-stops on an average 35mm SLR camera are:
1 • 1.4 • 2.8 • 4 • 5.6 • 8 • 11
• 16 • 22 • 32
- each F-stop admits half (or double) the light
of the previous one.
- Because the calculation for the AREA of a circle involves a square
function (pi times the radius squared), the f/numbers are actually the
*square roots* of a series of doubled numbers
1 (square root of 1)
1.4 (square root of 2)
2 (square root of 4)
2.8 (square root of 8)
4 (square root of 16)
5.6 (square root of 32)
8 (square root of 64)
11 (square root of 128)
16 (square root of 256)
22 (square root of 512)
32 (square root of 1024)
45 (square root of 2048)
64 (square root of 4096)
- f/2.8 (or f/1.4 if your lens is equipped with
it) is the widest aperture meaning it allows in the most light. Each
subsequent aperture allows in half as much light.
For instance in this example:
2.8 • 4 • 5.6 • 8 • 11 • 16 • 22
• 32
if we give the light admitted by f/2.8 the value of one then we may
look at it this way:
f/2.8 = 1 • f/4 = 1/2 • f/5.6 = 1/4 • f/8 = 1/8•
f/11 = 1/16
f/16 = 1/32 • f/22 = 1/64 • f/32 = 1/128
"stopping down" refers to allowing less light into the lens
therefore using a higher aperture such as from f/11 to f/16
"opening up" refers to allowing more light into the lens and
therefore using a lower aperture such as from f/8 to f/5.6
• APERTURE AS CONTROLLER OF DEPTH OF FIELD
- A change in aperture
size affects the sharpness of the image as well as the amount of light
entering the camera.
- The smaller an aperture (which means the higher
the f/number) the greater the overall clarity in the picture.
DEPTH OF FIELD - refers to the area of acceptable
sharpness in a photograph - the smaller the aperture the greater the depth
of field.
- CIRCLES
OF CONFUSION -the tiny circle of light formed by a lens as it projects
the image of a single point of a subject. The smaller the diameters
of all the circles of confusion in an image, the sharper the image will
be."circles of confusion" are
tiny circles of light formed by a lens as it projects the image of a
single point of a subject. The smaller the diameters of all the circles
of confusion in an image, the sharper the image will be.
- A"depth of field scale" often appears
printed on the lens as paired numbers that bracket the distances of
the nearest and farthest points of the depth of field.
- An example of changing depth of field: if a
row of pillars moving away from the photographer is photographed with
a lens set at f/22 more of it will appear in focus than if it were taken
at f/2.8
- THE
LENS
• LENS -a piece or several pieces of optical glass shaped to focus
an image of a subject
The
LENS
- LENS - the lens of a modern camera collects a large number of
light rays from a single point on an object and refracts, or bends, them
towards each other so that they converge at a single point
- Focal point: is the point of convergence described above
- Focal plane: is the plane on which the focal points fall
- Film plane: is the focal plane in a camera
• FOCAL LENGTH -is the distance between the lens and the focal plane
when the lens is focused on infinity.
- lenses are usually described as focal lengths (for example a 50mm lens
has a focal length of 50 mm)
- a wide angle lens will have a short focal length (ie 7.5mm)
- a wide angle lens increases the angle of view, and thus reduces the size
of objects within the image as compared to the size of objects within
an image formed by a normal lens
- a telephoto (narrow angle lens) will have a long focal length (ie 1000mm)
- a telephoto lens has a narrower angle of view and a greater magnification
than that of a normal lens
- normal-focal-length approximates human vision
- normal-focal-length changes depending on negative size, but for 35mm
negatives it is around 50mm
- distortions can be caused by all lenses, but are most apparent in wide
angle and telephoto lenses
• DEPTH OF FIELD
-a lens can focus on only one distance at a time. this is called the plane
of critical focus. Everything on the plane of critical focus will be in
focus (for instance if I focus on a car 10 feet away and near the car
is a person also 10 feet away from my lens then both will be in focus)
-there is an area preceding and following the plane of critical focus
which will appear in focus to the human eye
-the closer the plane of critical focus is to the camera the smaller the
depth of field
-the same aperture on a long lens will have a narrower depth of field
than on a short lens (for example f/8 on a 70mm lens will have a narrower
depth of field than f/8 on a 28mm lens) (this is because of RELATIVE APERTURE
- the aperture on a 70mm lens is actually bigger than the aperture on
a 28mm lens, but relatively they are the same, because they both allow
the same amount of light to reach the film plane)
• PERSPECTIVE -is the relative size and depth of objects within
the image
-perspective is controlled by the distance between the lens and the subject
-objects closer to the lens will appear larger in the picture in relation
to subj ects
farther awayndows will also be covered.
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