Sensitivity of film or sensor

The light sensitivity of film and the sensor is now predominantly in ISO specified. The number of common values is:

ISO 100 - 200 - 400-800

Here, the ascending sequence of numbers is not only mathematically, a doubling of the previous value, but a film with the next highest ISO rating is twice as light sensitive as the previous, in reverse order of half as sensitive to light.

The choice depends on the sensitivity of the first subject contrast from. Is the difference between light (not white) and shade (not black) in the motif very large, it therefore has a large number of finely differentiated shades, choose the higher sensitivity, because it has a flatter gradation exhibits and play thus finer detail in the situation. Accordingly, low subject contrast when one chooses a low sensitivity, because the gradation is steeper and has less differentiated nuances.

Increases with increasing sensitivity but at the appearance of his films graininess in digital cameras, the image noise . Therefore, should be sufficient and are elected only in exceptional situations, a low sensitivity, such as when documents scanned or contrast with creative viewpoint only a few details to be played or the recording light is too strong, high sensitivity, for most subjects, a mean value from the above series of numbers when the recording light is too weak.

If the sensitivity of the recording medium once firmly determined, only the values of aperture and exposure time.
Aperture is usually made even a single thin plate opening formed in the lenses , whose diameters are often enlarged by turning a ring on the outside of the lenses or zoom can. Then said aperture , the ratio of aperture to focal length of an optical system. A telephoto lens for example from 50 mm free aperture (D) and 200 mm focal length (f) has the diaphragm D: f = 50: 200 = 1: 4, also f / written 4th The opening itself is in contrast to other optical devices in the photographic lens is not specified because it is for the photographic practice without any further meaning. Called only focal length and aperture, ie: 200 mm - f / 4, where the panel stated (here 4), the largest of the adjustable lens and thus its luminosity known. Conventional panels are:

f / 1,4 - 2 to 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22

Here are small f-numbers - so big openings - only achievable with fixed focal lengths. Intermediate stages are possible, as many zoom lenses have a maximum aperture of f / 3.5, which corresponds to the level between 2,8 and 4.

Since the aperture is a reciprocal value, represents a large, wide-open aperture, a small aperture and a small, tightly closed aperture a large aperture. In the specified order from level to level, the aperture of the lens and thus halve the exposure to the recording medium acting, doubled in the reverse order. We are talking about the difference in the exposure that comes with adjusting to a panel concluded, as the aperture value, and exposure value (EV) called. Thus corresponds to an aperture of a light sensitivity level. Therefore, a picture can, for example, which was exposed at ISO 400 and aperture 16 may be made at a constant exposure time exposure with the same result even with ISO 200 and aperture 11th

The panel serves not only the exposure, but it also defines the depth in the image. Should stand out from the object to be photographed blurred background, choose a large aperture. If, by contrast from foreground to background in the field are equally into it, take a small aperture.

The stopping of a lens can not be operated at will, because its optical resolution is proportional to its aperture ratio (D f). The larger the aperture and the smaller the focal length, the greater the resolution. With the closing of the aperture is at a constant focal length and therefore the resolving power of the lens is reduced. The situation is similar with the resolution of a film or sensor, which corresponds to its granularity or the number of its pixels. The more fine-grained the better the resolution. Comparing the resolving power of the lens and the medium together, it usually arrives at aperture 16 in the range where the resolution of the lens undermines the resolution of the recording material. General Image blur is the result.


Author:

PPTPhotography.net charlotte wedding photographer & wedding photographer charlotte, one of the finest charlotte Wedding Photographers. To know more visit http://www.pptphotography.net/