18 July 2011

Common Photography Terms

18 July 2011

Automatic Exposure; Three kinds are available: programmed auto exposure, aperture-priority auto exposure and shutter-priority auto exposure.

AE Lock
Used to hold an automatically controlled shutter speed and/or lens aperture, in case you need to recompose your picture but want to retain an previous exposure reading.

AF (Autofocus) Lock
Used to prevent autofocus operation once the subject is in focus. This gives you more creative control by allowing you to focus, compose your image, and then capture the image.

Angle of View
The area of a scene that a lens can cover. The focal length of the lens determines the angle of view. A wide-angle (short-focal-length) lens includes more of a scene than a standard (normal-focal-length) lens or telephoto (long-focal-length) lens. Angle of view is basically the angle at which light rays can pass through the lens to produce an image on the film.

The aperture is the opening formed by the blades of the iris or diaphragm in the lens, through which light passes to expose the film. Aperture size is usually given in f-numbers, the larger the number, the smaller the opening. Aperture size together with shutter speed determine the amount of light falling on the film (exposure). The aperture is sometimes called the “stop".

Aperture Priority
An exposure mode on an automatic or autofocus camera that lets you set the aperture while the camera sets the shutter speed for proper exposure. If you change the aperture, or the light level changes, the shutter speed changes automatically.

Aspherical lens
A lens with a curved, non-spherical surface. Used to reduce aberrations and achieve a more compact lens size. With a spherical lens, rays traveling from the lens periphery create the image before the ideal focal point and give a blurred image center. With an aspherical lens, even the rays traveling from the lens periphery converge at the ideal focal point, thus producing a sharp image.

B (Bulb) Setting
 A shutter-speed setting on an adjustable camera that allows for time exposures. When set on B, the shutter will stay open as long as the shutter release button remains depressed.

    Light coming from behind the subject, toward the camera lens, so that the subject stands out vividly against the background. Sometimes produces a silhouette effect.

Best explained as the photographer taking numerous photos of the same thing using a variety of different camera settings. Bracketing is great when you are struggling to get a shot with exposure you like and that suits the image generally and helps ensure correct exposure of a photo when lighting in a scene is difficult.
Camera Shake
Caused by even a slight movement of the camera as it records an image. Camera shake is the main cause of blurred images.

Candid Pictures
Unposed pictures of people, often taken without the subject's knowledge. These usually appear more natural and relaxed than posed pictures.

Close-Up Lens
A lens attachment placed in front of a camera lens to permit taking pictures at a closer distance than the camera lens alone will allow.

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.

Color Balance
How a color film reproduces the colors of a scene. Color films are made to be exposed by light of a certain color quality such as daylight or tungsten. Color balance also refers to the reproduction of colors in color prints, which can be altered during the printing process.

Color Noise
Better known as chrominance signal-to-noise ratio. A measure of how accurately the color signals are reproduced. Poor chroma signal-to-noise ratios are evidenced in color fringing on edges of objects and what appears to be thousands of moving dots in large areas of highly saturated colors (especially red).

Color Output
The playback output level of the color (chrominance) signal after it is separated from the luminence signal. As with RF output, a low performing tape can lose color resolution due to increased percentage of noise.

The pleasing arrangement of the elements within a scene-the main subject, the foreground and background, and supporting subjects.

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.

Depth of Field
Refers to how much of a photo is in focus when the camera is focused on the main subject. Depth-of-field is controlled by a camera's aperture, in conjunction with the focal length of the lens. Deep (more) depth-of-field means that all or most of the picture is in focus from front to back. Shallow (less) depth-of-field means that a subject is in focus but objects in front and behind it appear out of focus. Depth of Field

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.

Diffuse Lighting
Lighting that is low or moderate in contrast, such as on an overcast day.

Softening detail in a print with a diffusion disk or other material that scatters light.

Digital Zoom
This is a common term for small video cameras and digital cameras. Digital zoom is electronic zoom where the camera interpolates the sensor readings to simulate a zoom.. Many people consider this to be a poorer quality image. Also see Optical Zoom

Double Exposure>
Two pictures taken on one frame of film, or two images printed on one piece of photographic paper.

Electronic flash
Designed to provide light where the lighting on the scene is insufficient. Electronic flash requires high voltage, usually obtained through batteries and a voltage-multiplying circuit which discharge a brief, intensive burst. Generally considered to have the same photographic effect as daylight. Modern flash units have multiple TTL exposure control functions and auto focus control.

Exchangeable Image File - Data that is stored in jpeg and TIFF image files, such as shutter speed, date and time, focal length, exposure compensation, metering pattern and if a flash was used a the time a photo was taken. EXIF data is very use when you are evaluating your photography.

Exposure Compensation
Increase or decrease the exposure an image from the exposure automatically selected by a camera metering system (see bracketing).

Exposure meter: Built-in digital camera meter that measures the amount of light when framing a photo and determines the best exposure. Matrix (Evaluative), Spot and Center-weighted are the main metering types; some digital cameras have all three.

F-numbers or F-stops
Numbers on the lens aperture ring and the camera's LCD (where applicable) that indicate the size of lens aperture. The lower the number the larger the aperture. As the scale rises, each number is multiplied by a factor of 1.4. Standard numbers are 1.0,1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc., each change resulting in a doubling or halving of the amount of light transmitted by the lens to the film. The actual value is represents a relationship between the focal length of the lens. f numbers are calculated by dividing the focal length of the lens by the effective diameter of the aperture.

Exposure consisting of a combination of flash and "available light" balanced to produce a pleasing mix of the two.

Film Speed/ISO/ASA
ISO stands for International Standards Organization and numbers such as ISO 100 or ISO 400 etc. Film was always manufactured to be at a certain ASA. Digital cameras give you the ability adjust your sensitivyt to light or ISO. The higher the number, the more sensitive or faster the film. Basically, the slower the film (low ISO No.) the sharper and clearer the photograph. Grainy effects can be achieved with fast films (high ISO No.).

In a digital camera a higher ISO setting will mean the sensor is more sensitive to light and can allow faster shutter speeds.  The negative side to this is that higher ISOs sometimes produce images that are noisy with digital grain.

An ultra-wide angle lens which purposely introduces barrel distortion so straight lines near the edges of the frame appear to curve out.

A colored piece of glass or other transparent material used over the lens to emphasize, eliminate, or change the color or density of the entire scene or certain areas within a scene.

Describes a non-adjustable camera lens, set for a fixed subject distance.

Fixed-Focus Lens
A lens that has been focused in a fixed position by the manufacturer. The user does not have to adjust the focus of this lens.

Image degradation caused by stray light which passes through the lens but is not focused to form the primary image. Often caused by light bouncing off internal air-to-glass surfaces.

Flash sync speed

Most modern cameras have two shutter panels, a top and a bottom one. When you press the shutter button, the top one starts to raise, and then the bottom one starts to follow, till the both meet and light is shut out. The speed you set your shutter will determine the time between when the top door starts moving and the bottom door follows (your camera make/model also can affect this).

Your max sync speed is essentially the setting at which the top door has reached the top of the sensor before the bottom door has started moving. It provides an entirely unobstructed view of the sensor for the flash to come in. A flash's duration is around 1/4000 or higher, so it will always be fast enough to hit the sensor for only a fraction of your shutter duration.
Your camera has a maximum "sync speed" at which time the panels are separated. However, some flash units have special modes which allow you to go beyond the "sync speed"

Focal Length
The distance from the film to the optical center of the lens when the lens is focused on infinity. Focal length on most adjustable cameras is marked in millimeters on the lens mount. On 35mm-format cameras, lenses with a focal length of 50mm are called normal or standard lenses. Lenses of 35mm or less are called wide angle lenses and lenses of 85mm or more are called telephoto lenses. Lenses which allow varying focal lengths without changing focus are called zoom lenses.

Focal Plane Shutter

A focal plane shutter exposes the image by moving two light-blocking curtains across the front of the image sensor. The first curtain slides open to begin the exposure, then the second curtain slide closed to terminate the exposure. In order to expose the picture from a flash, both curtains must be open at the time the flash is fired.

One individual picture on a roll of film. Also, tree branch, arch, etc., that frames a subject.

One or more pieces of optical glass or similar material designed to collect and transfer rays of light to form a sharp image on film, paper or a projection screen. In practical photography, compound lenses made of a number of elements of different types of glass are used. This enables the manufacturer to correct most of the faults (aberrations) found in simple lenses and provide images that are sharp across the whole picture.

Lens Shade
A collar or hood at the front of a lens that keeps unwanted light from striking the lens and causing image flare. May be attached or detachable, and should be sized to the particular lens to avoid vignetting.

Lens Speed
The largest aperture(smallest F-stop) at which a lens can be set. Fast lenses transmit more light and have larger openings than slow lenses. Determined by the maximum aperture in relation to focal length. Lens speed is relative: a 400 mm lens with a maximum aperture of F/3.5 is considered extremely fast, while a 28mm F/3.5 lens is considered to be quite slow.

Macro Focusing
Macro focusing, applied to zoom lenses, moves the lens group(s), enabling the lens to focus closer than the normal focusing distance from close-up shooting.

Optical Zoom
A true zoom. The focal length of the lens extends and retracts so an image is magnified by the lens itself. Whatever the focal length of the lens, image resolution stays the same. Optical zooms produce the best photo quality (see digital zoom).

Improper exposure causing an image to look too light. There is a loss of detail in bright areas.

This refers to following a subject with your camera. If you are photographing a runner you would want to follow the runner with the camera. Done correctly, your subject will be in focus and the background will show motion. This adds motion to a photograph.

Perspective is a two-dimensional representation of a three-dimensional scene. In photography this can be achieved by viewing 3-D objects from an angle rather than head-on. A photograph is also given perspective if there are objects in the foreground, middle distance and background, giving the whole scene “depth". For most photographers perspective refers to the relationship of the subject to the camera sensor or film plane.

Prime Lens
A lens that has one focal length. For example 135 mm lens is a prime lens.

An additive color model that starts with black, the absence of light. Computer monitors emit a combination of three colors: red, green, and blue to create a full color display.

A word with many meanings. In digital imaging, it most often refers to the number of pixels per inch in an image file. It can also refer to printer resolution, digital camera CCD resolution, etc. In traditional photography, if refers to the ability of a lens or photographic material to reproduce small details and is measured in lines per millimeter.

The intensity, or vividness, of a color. Increasing saturation makes colors in photos look richer. The amount of saturation can be adjusted in some cameras. It can also be increased or decreased with image editing software.

Shutter Lag:
The delay that takes place between pressing the shutter-release button and the time a photo is actually taken. Shutter lag times vary from digital camera to digital camera. Often the less expensive the camera the longer the lag.

Shutter Speed
The shutter speed is the length of time that the light capture medium is open to the light. 1/30 is 1/30 of a second. Try to keep your shutter speed 1/90 - 1/125 or faster to avoid camera blur. Anything less than 1/60 and you will need to either use a tripod or be very aware of your camera movement. It all depends upon you. For some, 1/60 may be too slow a shutter speed while others can work at 1/25th. Also note that the longer the focal length, telephoto vs wide angle lens, the more camera movement will affect image sharpness.

To obtain a blur effect on running water a slow shutter speed is needed. Depending on the amount of flow, 1/15 - 5 seconds is usually sufficient. To do this successfully it is necessary to use a tripod to eliminate camera shake.

If you wish to obtain a crisp image of a moving object then you will need a fast shutter speed of at least 1/250 or higher.

Light striking the subject from the side relative to the position of the camera; produces shadows and highlights to create modeling on the subject.

Single-Lens-Reflex (SLR) Camera
Light entering the camera through the lens is reflected up by a mirror behind the lens onto a ground glass screen above. This screen is viewed through the viewfinder and a glass pentaprism which turns the image the correct way up. Other camera functions such as light metering and flash control also operate through the camera lens.

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.

A condition in which too little light reaches the film or camera sensor. In general digital handles underexposure better than negative film. Underexposed film will producing a thin negative, a dark slide, or a muddy-looking print.

A fall-off in brightness at the edges of an image, slide, or print. This can be caused by poor lens design, using a incorrect lens hood, or attaching too many filters to the front of the lens.

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.

Zoom Lens
A lens in which you adjust the focal length over a wide range. In effect, this gives you lenses of many focal lengths.
Related lessons:
Aperture and f/16 Rule
Shutter Speed Basics

Depth of Field
Focused Bracketing or Photo Stacking 

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