Glossary

Analog v. Digital Signal

An analog signal continuously changes over time with respect to a reference level or standard; while a digital signal changes in regular steps, the signal level at each step represented by a number. Analog-to-digital signal conversion (as in PC image capture boards) involves sampling an analog signal at high frequency and representing each sample level by a number, stored as binary data. CCD cameras output analog video signals unless explicitly specified as digital cameras, in which case analog-to-digital conversion takes place in the camera rather than in a computer.

Aperture

Lens opening. The hole or opening formed by the metal leaf diaphragm inside the lens or the opening in a camera lens through which light passes to expose the film. The size of aperture is either fixed or adjustable. Aperture size is usually calibrated in f- numbers-the larger the number, the smaller the lens opening. Aperture affects depth of field, the smaller the aperture, the greater is the zone of sharpness, the bigger the aperture, the zone of sharpness is reduced. The hole or opening formed by the metal leaf diaphragm inside the lens; controls amount of light and depth of field, prevents vignetting and reduces lens aberrations; the size of the aperture is indicated by its f-number, i.e., the ratio of the diameter of the opening to the focal length of the lens; a large aperture is indicated by a small numerical f-number.

ASA

American Standards Association. Group that determining numerical ratings of speed for US made photosensitive products. e.g. films. In 1982, its role and its influence was narrow down by the establishment of the ISO (International Standards Organization).

CCD (Charge-Coupled Device)

Two-dimensional self-scanning electronic analog imaging device. The rectangular imaging area consists of rows and columns of rectangular photosensitive pixels that accumulate and store electric charge. Each column is separated by a shift register, or masked charge storage area, to which pixel charge is transferred. Charge is read out of the device sequentially from the shift register (masked) as the photosensitive pixels (unmasked) collect charge for the next field. Pixel charge is then transferred to the shift register, and the cycle continues. (Compare with frame transfer cameras in which charge is transferred to an entirely separate storage array at one time, eliminating the dead space between active pixels.)

Coated Lens

A lens covered with a very thin layer of transparent material that reduces the amount of light reflected by the surface of the lens. A coated lens is faster (transmits more light) than an uncoated lens.

Contrast

The range of difference in the light to dark areas of a negative, print, or slide (also called density); the brightness range of a subject or the scene lighting. It may be also explained as tonal difference. More often used to compare original and reproduction. A negative may be said to be contrasty if it shows fewer, more widely spaced tones than in the original. Or another way to explain, a difference in visual brilliance between one part of the image and another; without contrast, there would be no such thing as a visible image; a line in a photograph is visible only because it is either darker or lighter in tone than the background; every distinguishable part of the image is the result of a contrast in tonal values.

C v. CS mount

Threads are identical on these mounts: 1" diameter x 32 threads per inch. C mount uses 17.52 mm flange back distance; CS mount uses 12.5 mm. CS mount cameras can be converted to C mount by using a 5mm spacer element; however, CS mount lenses cannot be used with C mount cameras.

Cyan

Blue-green color, the complement of red.

Depth of Field

The zone of acceptable sharpness in front of and behind the subject on which the lens is focused; extends approx. one-third in front of and two thirds behind the in-focus subject; dependent on three factors: aperture, focal length, and focused distance; the wider the aperture, the longer the focal length, and the closer the focused distance, the less the depth of field, and vice versa; in comparison to a normal lens, wide angle lenses have inherently more depth of field at each f-number and telephoto lenses have less. Since this element is very important, another simpler way to explain is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph. Depth of field depends on the lens opening, the focal length of the lens, and the distance from the lens to the subject or can explain as in simpler term as the zone of sharpest focus in front of, behind, and around the subject on which the lens is focused; can be previewed in the camera - very handy for critical work.

Depth of Focus

The distance range over which the film could be shifted at the film plane inside the camera and still have the subject appear in sharp focus; often misused to mean depth of field.

Diffraction

When light is obstructed by an object and the wave front is changed, interference occurs between components of the altered wave front. The pattern formed by interference is called the diffraction pattern. Many components are designed to yield very specific diffraction effects (diffractive optics, gratings). Other components attempt to counteract this process to determine more information about the obstructing medium (electronic imaging).

Electronic Flash

Light source based on electrical discharge across two electrodes in a gas-filled tube. Usually designed to provide light approximating to daylight.

Exposure

The quantity of light allowed to act on a photographic material; a product of the intensity (controlled by the lens opening) and the duration (controlled by the shutter speed or enlarging time) of light striking the film or paper. The act of allowing light to reach the light-sensitive emulsion of the photographic material. Also refers to the amount (duration and intensity) of light which reaches the film.

Film Speed

Indicated by a number such as ISO 100 or ISO 400 etc. The sensitivity of a given film to light,. The higher the number, the more sensitive or faster (and more grainer) the film. Note: ISO stands for International Standards Organization.

Flash

The artificial light source in the dark. A brief, intense burst of light from a flashbulb or an electronic flash unit, usually used where the lighting on the scene is inadequate for picture-taking. Most flash will correct the color temperature back to 5000 Kelvin - the daylight color. Can play around with filters mounting on the flash head for some specific effects.

Flange Back Distance

Distance from the front of the camera mount thread, or flange, to the CCD image plane.

Flash Bulb

Light source based on ignition of combustible metal wire in a gas filled transparent envelope. Popular sizes are usually blue-coated to give light approximating to daylight.

Float Glass

Glass manufactured by the float process, which involves floating glass on liquid tin as the glass cools.

F-Number

A number that indicates the size of the lens opening on an adjustable camera. The common f-numbers are f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22. The larger the f-number, the smaller the lens opening. In this series, f/1.4 is the largest lens opening and f/22 is the smallest. Also called f-stops, they work in conjunction with shutter speeds to indicate exposure settings. Also can be explained as numerical expression of the relative aperture of a lens at its different stops; equal to the focal length divided by the effective aperture of the lens opening and written in various forms, such as f/8, f8, 1: 8, etc.; each f-number is 1.4 times larger than the preceding one; each number indicates a halving or doubling of the amount of light allowed to pass through the lens; the next higher numbered f-number sign) fies an aperture which lets in exactly one half as much light, and the next lower number, twice as much light, i.e., f/11 lets in half as much light as f/8, while f/5.6 lets in twice as much; all lenses stopped down to the same f-number produce images of equal illumination (apart from differences due to varying reflection losses); therefore, for a given shutter speed, a given f-Number always corresponds to the same exposure.

Focal Length

The distance between the film and the optical center of the lens when the lens is focused on infinity. The focal length of the lens on most adjustable cameras is marked in millimeters on the lens mount. The distance from the principal point to the focal point. In 35mm-format cameras, lenses with a focal length of approx. 50mm are called normal or standard lenses. Lenses with a focal length less than approx. 35mm are called wide angle lenses, and lenses with a focal length more than approx. 85mm are called telephoto lenses. Lenses which allow the user to continuously vary the focal length without changing focus are called zoom lenses .

Focus

Adjustment of the distance setting on a lens to define the subject sharply. Generally, the act of adjusting a lens to produce a sharp image. In a camera, this is effected by moving the lens bodily towards or away from the film or by moving the front part of the lens towards or away from the rear part, thus altering its focal length.

F-stop

A fraction which indicates the actual diameter of the aperture: the "f" represents the lens focal length, the slash means "divided by," and the word "stop" is a particular f-number; for example, with a 50mm f/1.4 lens, the actual diameter of its maximum aperture is 50mm divided by 1.4 or 35.7mm; at f/2, the diameter becomes 50mm/2 or 25mm; at f/2.8, the aperture is 50mm/2.8 or 17.9mm across; as the numerical value of the f-stop increases, the aperture decreases in size.

Grain

Minute metallic silver deposit, forming in quantity the photographic image. The individual grain is never visible, even in an enlargement, but the random nature of their distribution in the emulsion causes over-lapping, or clumping, which can lead to graininess in the final image. Also cross check with below for graininess.

Graininess

The sand-like or granular appearance of a negative, print, or slide. Graininess becomes more pronounced with faster film and the degree of enlargement.

Hi8

Video recording format, also refer a High Band 8mm format.

High Contrast

A wide range of density in a print or negative.

ICF (IR Cut Filter)

A special filter used for blocking infrared rays. In-between the optical lens and the CCD, most modern camcorders and digital cameras have this filter to compensate the colorings and the tones of the information reaching from subjects.

Image

Two-dimensional reproduction of a subject formed by a lens. When formed on a surface, i.e. a ground-glass screen, it is a real image; if in space, i.e. when the screen is removed, it is an aerial image. The image seen through a telescope optical viewfinder, etc. cannot be focused on a surface without the aid of another optical system and is a virtual image.

Incident light

The light from any source or the light falling on a surface as opposed to the light reflected by it.

ISO Speed

The international standard for representing film sensitivity. The emulsion speed (sensitivity) of the film as determined by the standards of the International Standards Organization. In these standards, both arithmetic (ASA) and logarithmic (DIN) speed values are expressed in a single ISO term. For example, a film with a speed of ISO 100/21¡Æ would have a speed of ASA 100 or 21 DIN. The higher the number, the greater the sensitivity, and vice versa. A film speed of ISO 200 is twice as sensitive as ISO 100, and half that of ISO 400 film.

LCD (Liquid Crystal Display)

An electronically generated text, numeric & symbols. Before the popularity of the LCD, LED is the most common method. LCD consume only one fifth (1/5) of the power of the LED and thus have a wider application in photographic line. The only problem is, it'll turn dark at very high temperature (will resume to normal when cool down) and it will fades in extended time. Used most commonly on cameras that shows such information as remaining exposures, flash status and aspect ratio selected.

Lens

One or more pieces of optical glass or similar material designed to collect and focus rays of light to form a sharp image on the film, paper, or projection screen.

Lux

A measurement of the light intensity. One Lux in video means light level of a candle light. l Lux approximately equals to 10 footcandles (1 Lux = 10.764 fc).

Manual

User selects both shutter speed and aperture, following or ignoring the meter's recommendations to achieve the desired exposure.

Monochrome v. Color CCD

Color CCD cameras start with the same sensor chip as monochrome cameras, but they must be filtered with a stripe or mosaic color filter to reproduce color information. In the filtering process some spatial resolution is lost because the sensor essentially is not using every pixel for every color. Color cameras necessarily filter out infrared illumination.

Nanometer (nm)

Unit of length equal to 10-9 meters. Used to express wavelength of light.

NTSC

National Television Standards Committee. Standards for video broadcasting and recording in the US and Japan. PAL's the standard in Great Britain and the commonwealth countries. SECAM used in many countries in the European communities.

Over Exposure

A condition in which too much light reaches the CCD or film, producing a dense negative or a very bright/light print or slide.

PAL

Phase Alternation Line. System for minimizing hue errors in color transmission used in the EU.

PC

Personal Computer.

Pitch

The spacing between consecutive threads on a threaded part.

Pixel

Short for picture element, a pixel is generally a rectangular unit of a scene. With respect to CCD cameras, pixel count is not a measure of resolution.

Refraction

The term given for the bending of light rays that occurs at the interface between two materials with different indices of refraction. A higher index of refraction, results in a lower refracted angle.

Screen

In a camera. the surface upon which the lens projects an image for view finding and, usually, focusing purposes. In SLR cameras. almost universally a fresnel screen with a fine-ground surface. Often incorporates a micro prism or split-image rangefinder.

Sensitivity

Expression of the nature of a photographic emulsion's response to light. Can be concerned with degree of sensitivity as expressed by film speed or response to light of various colors (spectral sensitivity).

Shutter

Blades, a curtain, plate, or some other movable cover in a camera that controls the time during which light reaches the CCD or film.

Single-Lens-Reflex (SLR) Camera

A type of camera that allows you to see through the camera's lens as you look in the camera's viewfinder. Other camera functions, such as light metering and flash control, also operate through the camera's lens.

Stop

The relationship between the focal length of a lens and the effective diameter of its aperture. An adjustable iris diaphragm permits any ordinary photographic lens to be used at any stop within its range. Sometimes used synonymously with f-number as in "f-stop" A unit of exposure change.

SVHS

Super Video Home system. Clearer than the conventional VHS because it separates chrominance and luminance transmission signals.

Telephoto Lens

A lens that makes a subject appear larger on film than does a normal lens at the same camera-to-subject distance. A telephoto lens has a longer focal length and narrower field of view than a normal lens and have a shallower depth of field than wide angle lenses. But it can do isolation of subject and have a longer reach without going near to the subject. Life can be very difficult in sports and wildlife photography. Telephoto lens whose focal length is longer than the diagonal of the film frame; in 35mm photography, lenses longer than 50-5Bmm; also referred to as a "long" lens.

Threads

Threads are an integral part of mounting components. English notation is thread diameter (inches) - threads per inch. Metric notation is thread diameter (mm) x thread pitch (mm) (e.g. 42 x 0.75mm).

T mount

Metric photo mount; 42mm diameter x 0.75mm pitch. Used in our T-mount Integrated Mounting Components.

Tone

The degree of lightness or darkness in any given area of a print; also referred to as value. Cold tones (bluish) and warm tones (reddish) refer to the color of the image in both black-and-white and color photographs.

UV

The ultra violet ray. This is beyond the visible spectrum i.e. it's invisible electromagnetic radiation of the sunlight.

Viewfinder

Device or system indicating the field of view encompassed by the camera lens. The term is sometimes used as a description of the type of camera that does not use reflex or "straight-through" viewing systems and therefore has to have a separate viewfinder.

Visible Spectrum

The wavelength interval of the electromagnetic spectrum that corresponds to visible light, that is light that is sensitive to the human eye. The range commonly used is 430 to 690 nm.

Wavelength

The characteristic peak-peak measure of one cycle of an electromagnetic wave.

Wide-Angle Lens

A lens that has a shorter focal length and a wider field of view (includes more subject area) than a normal lens. Also can explained as a lens whose focal length is shorter than the diagonal of the film frame; in 35mm photography, lenses shorter than 50mm; also referred to as a "short" lens.

Working Distance

Distance from the front end of a lens system to the object under inspection.

Zoom

In the context of optics, zoom refers to a variable focal length system: the field of view can be changed without changes in working distance. A zoom is essentially a compromise in aberration and image quality over a range of focal length solutions; therefore, zoom systems do not theoretically yield the same level of performance at every focal length setting. In the context of computer-based image capture, zoom is a magnification (or demagnification) of the individual pixels in an image file that yields no additional resolution.

Zoom Lens

A lens in which you adjust the focal length over a wide range of focal lengths. Substituting lenses of many focal lengths. Zoom lenses whose focal length is continuously variable over a certain range without a change in focus; its focal length is changed by operating a separate zoom or a combination focusing/zoom ring; difficult type of lens to design and manufacture, very useful for the photographer on a budget or one who likes to travel light.