| Aberration. | | | | halving of the amount of light transmitted by the |
| The inability of a lens to produce a true image, | | | | lens to the film. |
| particularly at the edge of a photograph. | | | | Film Speed |
| Usually, the more expensive the lens, the better | | | | ISO stands for International Standards |
| its optical quality and the fewer aberrations. | | | | Organization and numbers such as ISO 100 or |
| Angle of View | | | | ISO 400 etc. give the sensitivity of film to light. |
| The area of a scene that a lens can cover. The | | | | The higher the number, the more sensitive or |
| focal length of the lens determines the angle of | | | | faster the film. Basically, the slower the film (low |
| view. A wide-angle (short-focal-length) lens includes | | | | ISO No.) the sharper and clearer the photograph. |
| more of a scene than a standard | | | | Grainy effects can be achieved with fast films |
| (normal-focal-length) lens or telephoto | | | | (high ISO No.). |
| (long-focal-length) lens. Angle of view is basically | | | | Flash sync speed |
| the angle at which light rays can pass through the | | | | Exposure time with a focal-plane shutter is |
| lens to produce an image on the film. | | | | measured from the moment the first curtain is |
| Aperture | | | | released until the moment the second curtain is |
| The aperture is the opening formed by the blades | | | | released. The instant the first curtain closes, the |
| of the iris or diaphragm in the lens, through which | | | | electrical contacts for X sync close and instantly |
| light passes to expose the film. Aperture size is | | | | fire the flash. |
| usually given in f-numbers, the larger the number, | | | | Focal Length |
| the smaller the opening. Aperture size together | | | | The distance from the film to the optical centre |
| with shutter speed determine the amount of light | | | | of the lens when the lens is focused on infinity. |
| falling on the film (exposure). The aperture is | | | | Focal length on most adjustable cameras is |
| sometimes called the "stop". | | | | marked in millimetres on the lens mount. On |
| Aspherical lens | | | | 35mm-format cameras, lenses with a focal length |
| A lens with a curved, non-spherical surface. Used | | | | of 50mm are called normal or standard lenses. |
| to reduce aberrations and achieve a more | | | | Lenses of 35mm or less are called wide angle |
| compact lens size. With a spherical lens, rays | | | | lenses and lenses of 85mm or more are called |
| travelling from the lens periphery create the | | | | telephoto lenses. Lenses which allow varying focal |
| image before the ideal focal point and give a | | | | lengths without changing focus are called zoom |
| blurred image centre. With an aspherical lens, even | | | | lenses. |
| the rays travelling from the lens periphery | | | | Lens |
| converge at the ideal focal point, thus producing a | | | | One or more pieces of optical glass or similar |
| sharp image. | | | | material designed to collect and transfer rays of |
| Chromatic aberration | | | | light to form a sharp image on film, paper or a |
| The inability of a lens to bring all light wavelengths | | | | projection screen. In practical photography, |
| (particularly red & blue) into the same plane | | | | compound lenses made of a number of elements |
| of focus, thus causing overall blur. Usually found in | | | | of different types of glass are used. This enables |
| regular large-aperture telephoto and | | | | the manufacturer to correct most of the faults |
| super-telephoto lenses. Not improved by reducing | | | | (aberrations) found in simple lenses and provide |
| aperture size. Can be corrected with low | | | | images that are sharp across the whole picture. |
| dispersion (ED, LD SD) glass. | | | | Lens Speed |
| Colour temperature | | | | The largest aperture(smallest F-stop) at which a |
| A method of expressing the colour content and | | | | lens can be set. Fast lenses transmit more light |
| quality of light and measured in Kelvin (K). | | | | and have larger openings than slow lenses. |
| "Photographic daylight" has a colour temperature | | | | Determined by the maximum aperture in relation |
| of about 5500K. Photographic tungsten lights have | | | | to focal length. Lens speed is relative: a 400 mm |
| colour temperatures of 3200K to 3400K | | | | lens with a maximum aperture of F/3.5 is |
| depending on their construction. | | | | considered extremely fast, while a 28mm F/3.5 |
| Depth of Field | | | | lens is considered to be quite slow. |
| The distance between the nearest and furthest | | | | Perspective |
| objects in a photograph that are considered to be | | | | Perspective is a two-dimensional representation of |
| acceptably sharp. Dependant on aperture, focal | | | | a three-dimensional scene. In photography this can |
| length and focused distance. The smaller the | | | | be achieved by viewing 3-D objects from an |
| aperture, the wider the lens and the further the | | | | angle rather than head-on. A photograph is also |
| focused distance, giving a greater depth of field | | | | given perspective if there are objects in the |
| and vice versa. | | | | foreground, middle distance and background, giving |
| Electronic flash | | | | the whole scene "depth". |
| Designed to provide light where the lighting on the | | | | Single-Lens-Reflex (SLR) Camera |
| scene is insufficient. Electronic flash requires high | | | | Light entering the camera through the lens is |
| voltage, usually obtained through batteries and a | | | | reflected up by a mirror behind the lens onto a |
| voltage-multiplying circuit which discharge a brief, | | | | ground glass screen above. This screen is viewed |
| intensive burst. Generally considered to have the | | | | through the viewfinder and a glass pentaprism |
| same photographic effect as daylight. Modern | | | | which turns the image the correct way up. Other |
| flash units have multiple TTL exposure control | | | | camera functions such as light metering and flash |
| functions and auto focus control. | | | | control also operate through the camera lens. |
| F-numbers or F-stops | | | | Zoom Lens |
| Numbers on the lens aperture ring and the | | | | A lens which can be adjusted to a wide range of |
| camera's LCD (where applicable) that indicate the | | | | focal lengths without a change in focus, thus an |
| size of lens aperture. The lower the number the | | | | alternative for a number of individual lenses of |
| larger the aperture. As the scale rises, each | | | | various focal lengths. A difficult type of lens to |
| number is multiplied by a factor of 1.4. Standard | | | | design and manufacture, but very useful for the |
| numbers are 1.0,1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, | | | | photographer who likes to travel light. |
| 32, etc., each change resulting in a doubling or | | | | |