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Digital Photography Glossary
Photography Glossary - F
Understand the terminology of digital photography, digital printing and digital imaging so that you will become a better photographer. Photographic terms such as F/number, F/stop, Fill-in Flash, Focal Lenght, Focal Point, and more.
The f-number is the expression of the size of the aperture opening for a lens's given focal length. In its most basic terms, the f-number is the lens's focal length divided by the "effective" aperture diameter.
F/stop is the values on the lens barrel that indicate a specific aperture setting. The f-stop is the relative value for each individual lens, but does not denote the same size opening in each lens. Such that an f-stop of f/4.5 on a 25mm lens and 150mm lens, lets in the same amount of light, but the actual size of the aperture is much smaller on the 25mm lens than on the 150mm lens.
The fill-in flash isn't a separate flash unit, but rather a technique used when the background is much brighter than your subject, or the lighting is such that you have a high levels of contrast on your subject. As the name suggests, you use the fill-in flash to add fill light to the subject so it registers a more pleasing exposure. This is useful when the ambient light is overwhelming and would typically result in some level of silhouette. You'll want to turn on your flash when you're outside and meter the key part of your subject (i.e. a person’s face) that appears to be in "shadow" compared to the rest of the scene. Your image will be more balanced, and more pleasing.
Film is a gelatin acetate that is coated with light-sensitive metal halide crystals that when exposed to light transform and re-align themselves to "preserve" the image in the coating.
Film Speed is the international standard value that indicates a given film's sensitivity to light. Film Speed also indicates the grain level for a given film, as the more sensitive the film is to light (higher film speed), the coarser grain and lower image quality the film will have. Film Speed is interchangeable with the term/concept ISO (when relating to digital cameras).
Lens filters are transparent or translucent glass or gelatin elements that attach to the front of a lens. They protect the camera lens, alter the characteristics of light passing through the lens or add special effects and colors to an image. They come in two types -- screw-in filters and slot-in filters.
A Fixed Focal-length lens has a set focal length, measured in millimeters. A fixed focal-length lens is also called a "prime lens." Fixed focal-length lenses are markedly sharper than zoom lens, because they employ a lower number of lens elements so therefore the machining of the glass can be that much more precise.
Flare or lens flare, is a photographic phenomenon in which a light source enters the lens at a specific angle, and causes a pluming effect with the light. It's caused by aberrations in the manufacture of the lens' glass elements.
Flash Extender is a device that can increase a flash's light output by up to 3 stops of light depending on one's flash zoom setting.
Flash Synchronization is the automatic process in which the camera's shutter speed is synchronized with the camera's flash, such that the flash fires as a precise moment during the opening and closing of the shutter to provide additional exposure light on a subject.
Also known as the hot shoe, the flash socket is the bracket that holds a dedicated flash unit in place on the camera and enables the camera's automatic functions to synchronize with the flash unit.
Focal Length is the specific length of the lens' frontal glass element going back to the rear element, measured in millimeters. Focal length of a lens also dictates the various image properties of a lens (i.e. a short, wide angle lens has completely different properties than a long, telephoto lens). The focal length also determines the amount of magnification a lens provides.
Focal Point is the point in which the light entering the lens converges on a single point to generate the image. It is the exact point where the lens gives maximum sharpness and is denoted in your camera's viewfinder with a circle or a set of brackets.
Focus Tracking refers to the automatic mechanical feature in which the camera's on-board computer calculates the relative speed of a moving subject in order to effectively focus the lens on the subject. Focus tracking enables the photographer to acquire tack-sharp, in-focus photos of moving objects. A favorite feature among sports photographers.
Front Lighting is a lighting technique in which the light sources (natural or artificial) are in front of the subject. Unfortunately, Front Lighting can result in flat images, particularly in portraits.
F-stop is the mathematical value of the size of the aperture; while the actual aperture hole varies in size depending on the focal length of the lens, the f-stop value allows for uniform understanding of how much light exactly travels through the lens to give the same exposure value, regardless of lens length.