Gdes 73 Terms

Term Notes
Shutter

A barrier that opens and closes to control the amount of time the film or light sensor is exposed to light.

pinhole.jpg

Diaphragm

A thin opaque structure with an opening (aperture) at its centre. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture. Used to regulate the amount of light that enters the lens.

Sometimes used in leau of a shutter in digital cameras.

Analogous to an Iris.

Iris Most modern cameras use a type of adjustable diaphragm known as an iris diaphragm, and often referred to simply as an iris.
Shutter Speed
  • The amount of time the shutter is open expressed in fractions of a second.
  • Each shutter speed is 1/2 times or 2 times as long as the previous or next shutter speed.
  • Each shutter speed lets in 1/2 times or 2 times the amout of light as the previous or next shutter speed.

Typical whole shutter speed scale:

1sec 1/2 sec 1/4 sec 1/8 sec 1/15 sec 1/30 sec 1/60 sec 1/125 sec 1/250 sec 1/500 sec 1/1000 sec 1/2000 sec

shutter_speed.jpg
panning.jpg

Aperture

The diameter of the opening in the diaphragm

large_aperture.jpg
small_aperture2.jpg

F Stop

A number derived from the focal length of the lens divided by the aperture diameter.

Used to set the aperture, which controls the size of the opening for light to pass through.

Each larger f stop number describes a smaller aperture that lets through 1/2 the light of the previous whole f stop.

Each smaller f stop number describes a bigger aperture that lets through 2 times the light of the previous whole f stop.

Typical whole fstop scale:

f1.4 f2 f2.8 f4 f5.6 f8 f11 f16 f22 f32

fstop.jpg

Program/Auto Mode The camera selects both the aperture and the shutter speed.
Shutter-Priority Mode You set the shutter speed, and the camera sets the aperture.
Aperture-Priority Mode You set the aperture, and the camera sets the shutter speed.
Manual Mode You set the aperture and the shutter speed.
ISO/ASA

A standard number used to rate Film Speed.

Also used to describe sensitivity of light sensors.

As ISO doubles, so does light sensitivity.

CCD

Charge-coupled Device.

The image sensor.

Focus

No lens is perfect.

The subject is composed of small points at various distances.

Each point is small disc called circle of confusion.

When they are small enough, the eye sees them as points, and that part of the image will appear to be sharp (in the depth of field).

The larger the circles of confusion, the more likely an object will be out of focus. Points located in front or back of point have larger circles, and appear out of focus.(Depth of Field)

Longer focal lengths have larger relative aperture and resulting larger circles of confusion.

The nearer you are to the subject, the more critical is the focus.
Focal Length

The distance from the point where the light makes its last bend after passing through the lens element (called the rear nodal point) to the point at which the light focuses perfectly onto the film(called the focal plane) when the lens is focussed at infinity.

Focal length effects magnification and angle of view

A longer lens has more magnification and less angle of view.

The shorter the focal length of the lens, the greater the depth of field

focal_length_chart.jpg
focal_length_long_short.jpg
hyperfocal.jpg
long_lens.jpg
long_short.jpg
long_short_portrait.jpg
same_diff_focal_length.jpg
same_image_different_settin.jpg
wide_close.jpg

Depth of Field

The range of distance in front of and in back of the subject that objects still appear sharp.

More depth of field sometimes refered to as deeper depth of field.

Less depth of field sometimes refered to as a more shallow depth of field.

depth_of_field.jpg
perspective.jpg

Levels A dialogue in Photoshop which allows you to adjust brightness and contrast.
Gain

Increases the sensitivity of the image sensor.

Can result in noise(stray pixels of incorrect colors).

bit depth

The amount of digital information used to store the color of a pixel

8 bits=256 colors

bit_depth_graph.jpg

angles of view The amount of a scene that is visible in an image.
hyper focal distance Setting a camera for maximum depth of field at a given f-stop.
zoom A lens with variable focal lengths.
telephoto

A focal length longer than a normal lens.

Has less depth of field

Tends to flatten image(distances look compressed)

wide angle

A focal length shorter than a normal lens.

Has more depth of field

Tends to distort image as focal length gets shorter.

interpolation Deriving pixels from nearby pixels.
RGB Red, green and blue.
Resolution The number of pixels per inch(example:72 dpi) or the number of total pixels on an image(example:3.5 megapixels)
Color Channels

greyscale areas for color separations.
Amount of white is how much color appears

additive_colors.gif

Pixels Picture Elements
CMOS

Complementary metal-oxide semiconductor

Alternative to CCD based cameras.