NSL Photography's™ Glossary of Photographic Terms - F

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F-number, f/stop or f/setting
The numbers on the lens aperture ring and the camera's LCD (where applies) that indicate the relative size of the lens aperture opening. The f-number series is a geometric progression based on changes in the size of the lens aperture, as it is opened and closed. As the scale rises. each number is multiplied by a factor of 1.4. The standard numbers for Calibration are 1.0,1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc., and each change results in a doubling or halving of the amount of light transmitted by the lens to the film or sensor plane. It's calculated from the focal length of the lens divided by the diameter of the bundle of light rays entering the lens and passing through the aperture in the iris diaphragm.

A method of flash photography that combines flash illumination and ambient light, but does not attempt to balance these two types of illumination. The light from the flash is used to soften or fill in the shadows or dark picture areas caused by the brighter main light.

A photographic emulsion coated on a flexible, transparent base that records images or scenes.

Film Speed
Indicated by a number such as ISO 100 or ISO 400 etc. It is 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.

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

Fisheye Lens
Ultra-wide angle lens giving 180 angle of view. Basically produces a circular image on 35 mm, 5-9 mm lenses showing whole image, 15-17 mm lenses giving a rectangular image fitting just inside the circle, thus representing 180 across the diagonal.

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, applies on most entry or disposable cameras.

Florite is a low dispersion mineral used as a substitute for glass in some highly corrected long focal length lenses. Canon uses most of these properties on its EF-L series long telephotos.

The artificial light source in the dark. Electronic flash requires a high voltage, usually obtained from batteries through a voltage-multiplying circuit. It has a brief, intense burst of light, usually used where the lighting on the scene is inadequate for picture-taking. They are generally considered to have the same photographic effect as daylight. Most flash will correct the color temperature back to 5000 kelvin - the daylight color.

Flash Bracket
It is generally comprised of one arm of the L-shaped bracket which extends under the camera body and uses the camera's tripod socket to mount the camera on the bracket. The vertical arm of the bracket serves as a handle and mounts a flash unit in an accessory shoe often on top of the handle portion, but there are other methods. Flash mounted in a bracket usually requires a separate electrical cord to make the electrical connection between camera body and flash unit.

Flash Exposure Bracketing
Enables a photographer to automatically bracket exposures at varied flash output levels, in TTL and iTTL flash shooting, without changing the shutter speed and/or aperture, this is a one of the top flash features which can only be found on upper level and pro cameras.

Flash Synchronization
Timing of the flash coincides with release of the camera's shutter. There are two types of synchronization: Front-Curtain Sync, which fires the flash at the start of the exposure, and Rear-Curtain Sync, which fires the flash at the end of the exposure.

Flash Sync Speed
Exposure time with a focal-plane shutter is measured from the instant the first curtain is released, to begin its travel across the frame, until the instant the second curtain is released, to begin its travel across the frame. When the first curtain reaches the end of its travel, the film frame or sensor is uncovered as far as the first curtain is concerned, so it closes the electrical contacts for sync and fires the flash instantly. Shutter speed is the time during which the entire film or sensor is exposed in flash shooting. Most modern camera with vertical travel shutter curtain have faster flash sync speed like 1/250 sec. or slower, while pro level cameras may sync at much higher speed using a custom Setting.

Flash Output Level Compensation
A control used to adjust TTL or iTTL auto flash operations, enabling an increase or decrease of flash output to lighten or darken the flash effect.

Flash Shooting Distance Range
The distance range over which a flash can effectively provide light.

Flash Memory Card
A storage medium used by digital cameras to store the camera's images, ie. a digital camera's film.

An overall decrease in contrast caused by light being reflected off, instead of transmitted through, a lens surface. This is somewhat controllable through the use of a multilayer coating of individual lens elements in a lens and it's aggravated by unclean lens surfaces on front and rear lens elements or filters.

Too low in contrast. The condition when the range in density in a negative, image or print is too short or in some cases, reflecting the low resolution produced by a low quality lens.

Flat Lighting
Lighting which produces very little contrast or modeling on the subject plus a minimum of shadows.

Flexible Program
Flexible Program function automatically selected shutter speed/aperture combination while maintaining correct 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 millimetres on the lens mount. Lenses which allow the user to continuously vary the focal length without changing focus are called zoom lenses.

Focal-Plane Shutter
An opaque curtain containing a slit that moves directly across in front of the film or sensor in a camera and allows image-forming light to strike the film or sensor.

Adjustment of the distance setting on a lens to define the subject sharply. 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.

Focus Range
The range within which a camera is able to focus on the selected subject - 4 feet to infinity, for example.

Focus-Priority for Autofocus
Under this setting the shutter will not release until the subject is in focus.

Focus Tracking
Enables the camera to analyze the speed of the moving subject according to the focus data detected, and to correctly focus by anticipating the subject's position and driving the lens to that position at the exact moment of exposure.

Darkening or discoloring of a negative, image or print or lightening or discoloring of a slide caused by exposure to nonimage-forming light.

The area between the camera and the principal subject.

Front-Curtain Sync
The flash fires an instant after the front curtain of a focal plane shutter has completed its travel across the film plane. This is the way the camera operates with the flash sync mode at Normal Sync.

An area of one image as defined by a negative, slide or sensor size.

Pattern of a special form of condenser lens consisting of a series of concentric stepped rings, each ring a section of a convex surface which would, if continued, form a much thicker lens. It is used on focusing screens to distribute image brightness evenly over the screen.

Frames per second. Used to describe how many photos per second the camera can take.

Free Working Distance
In close-up or macro photography, it is the distance between the front of the lens and the subject. It is an important consideration when photographing shy or dangerous subjects or when using supplementary illumination.

Fellow of the Royal Photographic Society of Great Britain. Most salon photographers dream to have a title on their belt. A recognition that a photographers' standard in photographic field.

One individual picture on a roll of film.

Light shining on the side of the subject facing the camera.

Full Aperture Metering
TTL and iTTL metering systems in which the camera simulates the effect of stopping down the lens when the aperture ring is turned, while leaving the diaphragm at full aperture to give full focusing screen brilliance. The meter must be "programmed" with the actual full aperture, and the diaphragm ring setting.

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