Exposure control in the master of understanding the basic concepts.

Prerequisite: "file" concept we all know, exposure mainly by the shutter and aperture control, both to file (stop) as a unit. .In the same light, doubling the shutter, or aperture increases to double the light falling on the double film. .Thus, the exposure profile to be defined in a straightforward unit. .By analogy, in a different light, the same aperture, prior knowledge: "file" concept <p> we all know, exposure, shutter and aperture control mainly, both to file (stop) as a unit. .In the same light, doubling the shutter, or aperture increases to double the light falling on the double film. .Thus, the exposure profile to be defined in a straightforward unit. .By analogy, in a different light, the same aperture, shutter if the difference between a file to obtain the same exposure on film, then the brightness of the light on the difference between the two of a file. .Then, the "file" can also be a measure of brightness units. .</ P> <p> order to approach such a numerical measure of brightness, so it defines a basic reference value: EV (exposure value). .If a light intensity recorded with ISO 100 film, shutter time is one second, aperture f/1.4 to achieve "proper" exposure, the brightness is defined as EV = 1. .Else the same, but the shutter into a half a second, the brightness of light is called EV = 2. .By analogy. .As a result, the whole scene brightness value can be used to represent EV. .EV value difference of 1, the exposure he sent a file. .</ P> <p> a scene, the brightness of different parts is clearly different. .Such as: white walls under strong sunlight, and shadows in the pile of black coal. .The reflected light from their brightness, and perhaps to a difference of ten to fifteen files. .If the sun is also screen, this brightness difference to know where to go, or thirty? .Forty file? .Not tried. .</ P> <p> film "dynamic range" </ p> <p> film can record the brightness of the scope is extremely limited. .Light to a certain extent that is all white, dark to a certain extent that is all black. .Brightness difference between the two limits is the film's dynamic range (dynamic range). .Typically, black and white of the DR about 15 stalls, the dynamic range of color negative film has 7-8 stalls, the dynamic range of color reversal film surface about 5 files. .</ P> <p> exposure control </ p> <p> the so-called exposure control, is actually very simple. .If the brightness of the scene painted into a vertical column in the brightest, the darkest in the next, any given exposure, but the vertical column in the box out of a window (see Figure). .Something in the box was recorded on film, outside of the box there is no black and white details. .How a box method, that is, exposure control, their skills in another paper talk. .The figure demonstrates the three different exposure, the main visible record in the brightness of the film is different. .</ P> <p> exposure tolerance: tolerance. .</ P> <p> to photos from the film, there is an exposure process. .Smaller dynamic range of photo paper, estimated at about 3-4 files. .India-phase process is similar reasoning exposure control: the dynamic range of photo paper on the film box, a small window: in this box to be printed on photo paper, non-reproduction outside the box is black and white. .Example of the figure two different film exposure: an accurate exposure, one overexposed. .The figure shows, the use of appropriate printed-phase exposure, had been exposed in the main body of the film or may be moved back to the gray, the original film in order to achieve correct exposure errors. .Photography permitted the exposure of error, the film is called "exposure latitude" (exposurelatitude). .</ P> <p> simple calculation can be found: To compare a correct exposure and the exposure of an error, if you want two in the final picture looks the same: black is black and white is white, gray is gray, the .the time of exposure photography allowed the error (ie, tolerance) in fact is equal to the dynamic range of film and photographic paper the difference of the half. .In terms of color photography, tolerance is about two steps. .That is why we often say: poor color photography, the exposure of a two steps are all right then. .Black and white photography, this tolerance is even greater. .(However, the exposure is not accurate, or there will be differences, the discerning eye can see it, mainly because some contrast, color reproduction due to the nonlinearity of such.) </ P> <p> here by tolerance, .or narrow sense. .By the above argument, there is no tolerance on the issue reversal film, because the film itself is the final product, no longer have the opportunity to correct later. .But usually it is referred to the word tolerance. .Tolerance in this sense, refers to the ability of our visual sense. .The more light the main, often a matter of opinion; exposure and poor in 1 / 3 of the file is not necessarily everyone could see that; seen by everyone not necessarily think there is a big deal. .We usually attributed to the difference between this "tolerance." .It is often said: tolerance reversal film is 1 / 3 to 1 / 2 files. .</ P> <p> above is talking about the exposure, the mechanism of the imaging process, but I think this is to understand and master the key exposure. .I hope this text faithful to the film will certainly be helpful to understand the exposure. .</ P> <p> I do not love reading, these are summarized in the individual's understanding and experience. .Turned over a few books, not seen where the system introduced. .Right not to invite you to correct me. .If you find a talking book which, if different, the books shall prevail; if the same, only that we understand correctly. .Ansel Adams never learned the regional exposure method, but it seems that the principle is similar to connected..