Nikon SLRs Series Instruction Manual

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Nikon SLRs Series Instruction Manual Manual pdf 10 page image

Setting the apertureTo preset the lens aperture, turn the knurled aperture ring on the lens barreluntil the desired f/number lines up with the black dot in the top center of themilled ring. The diaphragm can also be preset for intermediate aperturesbetween the click-stopped markings.Aperture and Depth of FieldThe lens aperture determines the amount of light which passes through the lensand strikes the film. It also influences depth of field. Apertures are expressedin f/numbers, with larger numbers representing smaller apertures. Forexample, f/4 is larger than f/8 and allows more light to reach the film. Eachf/number admits exactly twice as much light as the next largest number, sowhen the aperture is increased or decreased by one stop, the exposure timerequired is doubled or halved respectively. For example:Aperture f/1.4 f/2 f/2.8 f/4 f/5.6Relative Exposure Time (seconds) 1/500 1/250 1/125 1/60 1/30Depth of field refers to a zone extending in front of and behind the plane ofsharpest focus. Within this zone, blur (or unsharpness of the image) will benegligible and everything can be accepted as being in sharp focus. It extends agreater distance behind the subject in focus than in front. Depth of fielddepends on three factors: focal length of the lens, lens-to-subject distance andtaking aperture. The smaller the aperture and the shorter the focal length of thelens, the greater the depth of field (for example, wideangle lenses have moredepth of field than telephotos). Also, the closer the subject, the smaller thedepth of field. These three factors can be adjusted independently or incombination to give the photographer creative control over the final picture.By stopping down the lens only, the depth of field can be increased, asillustrated by the following three photographs:1.Lens at f/4. Small depth of field with only main subject in focus.