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Photographer's Glossary

Every field has its own continuously changing terms, acronyms, and definitions called lingo. Photography is no different as it acquires new technology, such as the transition from film cameras to digital cameras. When you get into the world of photography, it is always good to know the lingos. This glossary will help you understand the lingo in photography.

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Angle of Incidence - The angle at which the light rays strikes the surface.

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Angle of Reflection - The angle at which the light rays reflects from the surface. The angle of reflection equals the angle of incidence. Only applies to a specular reflection where the surface is uniform. In a diffused reflection, light is reflected in all different angles.

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Aperture - The lens opening that lets in light. The diameter of this opening, in addition to the focal length, determines the f-stop number. The f-stop number is sometimes referred to as the aperture number, or aperture for short. F-number is focal length divided by aperture diameter. Both units are in millimeters and the resulting f-number is unit-less.

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Aspherical Lens - A lens that is not spherical in shape. The technology to create non-sperical lenses wsa invented to reduce image distortion that is a common characteristic of a spherical lens. Aspherical lenses are generally molded out of plastic or the plastic coated onto the surface of a glass lens.

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Chromatic Aberration - Occurs when light rays travels through glass (or lens). Each light wave frequency bends (refracts) at a different angle while traveling through the lens. Short wavelengths (toward the blue) are refracted more than long wavelengths (toward the red). Thus, different color wavelengths are exposed on different portions of the photosensitive material (film or sensor). Achromatic lens solves this problem by combining lenses with different refractive indexes.

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Color Fringing - One of the effects of lateral chromatic aberration. It appears as magenta and green bands at contrast boundaries. Color fringing is always more apparent on the edge of the image than the center due to the lens curvature. It becomes the worst at the image corners.

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Depth-of-Field (DOF) - The distance range at which the subject acceptably sharp is defined as DOF. Depth-of-Field can be changed by changing the size of the aperture. A larger aperture (smaller f-number) causes narrow DOF range. A smaller aperture (larger f-number) creates a wide DOF range.

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Digital Sensor - When digital cameras came along, it replaced the original film with an image capturing device called a digital sensor. The digital sensor is a photosensitive device when charge. It captures an image through the lens and stores it as a digital photograph.

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Dispersion - The variation in a lens-element's ability to bend light.

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Exposure Latitude - The range of exposure at which the photosensitive material (film or sensor) will produce an acceptable image. Most slide films have small exposure latitude (in the 1-stop range). Most print films have big exposure latitude (in the 5-stop range), because exposure can be compensated in the printing stage.

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Film - A photosensitive material that can capture an image when exposed to light. The original camera focuses an image on the film plane using a lens. The photographer opens the shutter to expose the film to the light source. Then the shutter is closed. In a dark room, the film is developed (fixed so that it can no longer be changed by light exposure) into a photograph. Today's digital camera works in this similar concept.

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Focus - The action of bringing the subject into sharpness and clarity behind the camera. The original film cameras only have manual focus capability, meaning the photographer must rotate the lens until the subject comes in focus. Sometimes the action occurs so fast that it is difficult to achieve focus manually. Then auto-focus is invented. With auto-focus, the photographer holds the shutter button down half way and the camera will auto-focus on the subject that is under the auto-focus point. Many cameras today can switch between manual and auto-focus. Some low-end cameras only supports one mode.

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Image Stabilization - The ability to reduce blur through counteracting shake. there are two methods of image stabilization: digital and optical. The digital method uses software algorithm to stabilize the image via the digital sensor. The optical method uses gyros in the lens or on the physical sensor to eliminate shake. The optical image stabilization method is generally better than the digital image stabilization method.

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ISO - In photograhy, ISO refers to the light gathering capability of the photosensitivity material (film or sensor) used to capture the image. Because the International Organization of Standardization defined this standard, the name ISO speed has became synonymous to film speed. The sensitivity of the material increases as the ISO number increase. Every doubling of the ISO number is one stop increase in exposure. Every halving of the ISO speed is one stop decrease in exposure.

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Focal Length - With a pinhole camera, the focal length is the distance between the pinhole (serving as the aperture) and the film/sensor plane. An equivalent lens, with the same focal length as the pinhole, capturing an object will produce an object image that is the same size as the object image produced by the pinhole.

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Macro - Taking extreme close-up photographs of a subject, whether the subject is really small or capturing a very small part of a larger object. In both cases, the small subject is magnified to fill the image as much as possible.

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Memory Card - A storage unit that holds the captured photographs. It is inserted into the digital camera to capture the photographs. Then it can be taken out and inserted into your computer to move your photographs to your computer.

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Reflection - When light ray strikes a surface, it is bounced away from the surface. The act of being redirected from its original path is called reflection. Two types of reflection: specular and diffused. A specular reflection occurs when light is reflected from a smooth uniform surface, such as a mirror. In a specular reflection, the entire light wave continues to travel in the same direction after being reflected. A diffused reflection occurs when light is reflected from a rough, non-uniform surface. In a diffused reflection, the light wave is scattered in different directions due to the irregular surface.

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Refraction - The property that light exhibits when traveling from one transparent medium into another transparent medium, such as from air into water. When light travels from one medium into another, part of the light ray is reflected away from the second medium. Another portion of the light ray enters the second medium and is bent at the boundary. This bent ray in the second medium is called the refracted ray. The angle of the bent depends on the difference between the two mediums, the wavelength of the light ray, and the angle of incidence.

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