Nikon F75D Instruction Manual - Page 62

Glossary-continued Flexible Program Flexible Program function temporarily shifts an automatically selected shutter speed/aperture combination while maintaining correct exposure. That is, the desired shutter speed or aperture can be selected in Auto-Multi Program. f-number The f-number represents the aperture value and is calculated from lens' focal length divided by the effective aperture opening. The standard numbers for calibration are 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc. The smallest f-number is called maximum aperture and the largest f-number is called minimum aperture. Lenses with large maximum apertures (smaller f-numbers) are 'fast' lenses that allow photographers to use faster shutter speeds in dim light. Lenses with smaller maximum apertures (larger f-numbers) allow the use of lower shutter speeds for available light but are also lighter and smaller than faster lenses. With some zoom lenses, aperture varies depending on the focal length setting. Focal length The distance from the principal point to the focal point. In 35mm-format cameras, lenses with a focal length of approx. 50mm are called normal or standard lenses. Lenses with a focal length less than approx. 35mm are called wideangle lenses, and lenses with a focal length more than approx. 85mm are called telephoto lenses. Lenses which allow the user to continuously vary the focal length without changing focus are called zoom lenses. Focus Tracking Enables the camera to analyse the speed of a moving subject according to the focus data detected, and to obtain correct focus by anticipating the subject's position-at the exact moment of exposure. Lock-On™ Autofocus keeps focus firmly on a main subject during Focus Tracking even if some other object momentarily blocks it in the viewfinder. 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 F75/F75D operates with the flash sync mode at Normal Sync. (See "Rear-Curtain Sync".) Guide number The guide number indicates the power of a flash in relation to ISO film speed. The guide number of the built-in Speedlight of the F75/F75D is 12 (ISO 100, m). Guide numbers are quoted in either metres or feet. Guide numbers are used to calculate the f/stop for correct exposure as follows: guide number f/stop flash-to-subject distance Using a selected aperture, we can calculate the required flash-to-subject distance with the formula: guide number flash-to-subject distance = -------- f/stop Useful for determining the maximum flash-tosubject distance for flash photography. ISO film speed The international standard for representing film sensitivity. The higher the number, the greater the sensitivity, and vice versa. A film speed of ISO 200 is twice as sensitive as ISO 100, and half that of ISO 400 film. Vignetting Progressively diminished illumination on the film from the centre to the corners. There are two kinds of vignetting-natural vignetting caused by the lens, and vignetting that is caused by improper use of accessories such as a lens hood or filter. Metering system See the column on page 32. Rear-Curtain Sync Flash fires an instant before the second (rear) curtain of the focal plane shutter begins to move. When slow shutter speeds are used, this feature can create a blur effect from the ambient light, i.e., flowing-light patterns following a moving subject with subject movement frozen at the end of the light flow. (See "Front-Curtain Sync".) Slow Sync A flash technique for using the flash at a slow shutter speed. Flash shooting in dim light or at night at a fast shutter speed often results in a flash-illuminated subject against a dark background. Using a slower shutter speed with the flash brings out the background details in the picture. The F75/F75D's Slow Sync mode extends the automatically controlled shutter speed range down to 30 sec. (in Auto-Multi Program, Aperture-Priority Auto) or 1 sec. (in h Night Portrait mode). MISCELLANEOUS 122 www.mynikon.com.pl 123