Mar 28, 2018 Written by Pawan Negi Film speed
FILM SPEED: cinematography course Assignmnet no.1
1.Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometer and measured on various numerical scales, the most recent being the ISO system
2. A closely related ISO system is used to describe the relationship between exposure and output image lightness in digital cameras.
3.Relatively insensitive film, with a correspondingly lower speed index, requires more exposure to light to produce the same image density as a more sensitive film, and is thus commonly termed a slow film. Highly sensitive films are correspondingly termed fast films.
4.Slow-speed films generally refer to film with 100-200 ISO ratings. These slower speeds are excellent for outdoor landscape photography and inanimate objects.
5.Medium speed is 400 ISO. As can be expected, the medium speed is probably the best for general-purpose use and can handle indoor lighting conditions, overcast days and any combination of the two.
6.Fast-speed film is usually rated at 800 ISO and above. It's best for moving subjects you might see at a sporting event or concert, or when you plan on using a zoom lens or are shooting in a dimly lit area.
7.Film speed is found from a plot of optical density vs. log of exposure for the film, known as the D–log H curve or Hurter–Driffield curve. There typically are five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region.
8.Film speed is used in the exposure equations to find the appropriate exposure parameters. Four variables are available to the photographer to obtain the desired 9.effect: lighting, film speed, f-number (aperture size), and shutter speed (exposure time)
Upon exposure, the amount of light energy that reaches the film determines the effect upon the emulsion. If the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor by varying the camera's shutter speed and aperture, so that the energy received is the same, the film will be developed to the same density. This rule is called reciprocity.
10 .The film speed dial of the Canon A-1 (1978) supported a speed range from 6 to 12800 ASA (but already called ISO film speeds in the manual). On this camera exposure compensation and extreme film speeds were mutually exclusive.