Photography 1 ch 4

Exposure

Equivalent Exposures Exposure = Intensity (aperture) x Time (shutter speed). ______ is a combination of the intensity (brightness) of light that reaches the digital sensor or film (brightness is controlled by the size of the aperture) and of the length of time the light strikes that light-sensitive surface (duration is controlled by the shutter speed). The more light that reaches the film, the greater the buildup of silver density in the negative. In the same way, the more light that strikes the sensor in a digital camera, the higher the numerical level recorded at each point (or photosite) on the array. Regardless of whether you're working with a digital camera or with film, you can adjust the exposure of your pictures—and therefore their lightness or darkness—by changing the shutter speed, aperture, or both. An exposure is usually calculated by a light meter that measures the scene. It provides a combination of aperture and shutter speed that should expose your picture correctly. If your camera is automatic, it will set a combination for you. If you are using a manual camera, or your camera has a manual mode, you can set the aperture and shutter speed according to the light meter that is built into the camera—most cameras have one. A correct exposure combination can also come from a hand-held light meter, or from an educated (or lucky) guess. But you are not limited to this one combination, even though most meters built into cameras show you only one. There are many different correct-exposure combinations— for every photograph you take—that you could choose. Which combination you choose is one key to creative photography. Your choice determines how you decide to control depth of field (the sharpness of objects from near to far) as well as how much you decide to stop or blur motion. Cameras with built-in meters show only one combination of shutter speed and aperture produce a correct exposure. However, other combinations would also work. Around this circle is a set of different, but equivalent, exposures. You have a similar choice every time you make an exposure.

latitude, dynamic

Exposure Latitude and Dynamic RangeL How Much Can Exposures Vary? In very contrasty lighting, no film or digital sensor can record color and details simultaneously in very light highlights and very dark shadows because the range of tones in the scene is greater than the usable exposure range of the film or sensor. The usable exposure range of a specific film is sometimes called its ___; more precisely, the usable exposure range of film or a digital sensor (or a range of subject brightnesses) is called _____ range. When the dynamic range of a scene exceeds the dynamic range of the capture medium, you are likely to lose some detail. If the lightest areas are correctly exposed, the shadows will be too dark, the darkest of them compressed into black. If shadows look good, highlights will be similarly washed out and compressed into pure white. Try exposing for the most important part of the scene, then bracket additional exposures (see page 76) to make sure you have one exposure that achieves the best compromise. Sometimes, if the subject is not too large or too far away, you can use a reflector or a flash unit to add fill light to lower the contrast in a scene. With film, use color negative instead of reversal film (see the page opposite) if you know you'll be shooting in hard, or contrasty, light. It is easier to get good exposures if lighting is soft or flat, with relatively little difference between the lightest and darkest areas (see photograph, right). With such a scene it is less likely that areas will lose detail and be much too light or much too dark. Image-editing software can merge bracketed exposures, if neither camera nor subject moved between making any of the bracketed exposures. Using two or more exposures to ensure capture of a contrasty scene is called HDR, for high dynamic range (see page 134). Shooting in soft, diffused light is simpler than working in contrasty light because the range of tones from light to dark better fits the capture range of light-sensitive materials. Diffused light is also kind to the human face, creating soft shadows that are often more complimentary than the hard-edged, dark ones of direct light. The soft illumination of an overcast day supports the contemplative expression of a girl who, as D'Amato by her placement m frame, is caught between the spirit and the flesh. Negative films—color and black-and-white—have enough exposure latitude for most scenes. The best results are from a correctly exposed negative (center), but you will be able to get a passable image from even a badly overexposed or underexposed frame. Here, exposures on the strip of film varied by one stop between each frame. Color reversal (positive transparency or slide) film has little exposure latitude. Even a small amount of overexposure or underexposure is readily visible, especially when shadows and highlights measure more than (the optimum) five stops apart. Exposures on the strip of film above varied by one stop between frames. Below, both pages. Exposures from a digital SLR camera have slightly more latitude than negative film. These exposures varied by one stop between frames. Dynamic range, the span of tones that a digital camera can capture, is greater in some cameras than others.