We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
122
PRINCIPLES OF CINEMATOGRAPHY
OOOaQQQQOQaOODDaDQOaQQQQQQQDaOQQQODOOODQQQQQQOaai
/ppppopgggnggpgoononnQaggogonoooonooaannaoo.nnoooQi
Fig. 52. — A 2b sensitometric strip.
the light beam to modify the characteristics of the light to the required quality for testing purposes.
The increase in times in exposure which are given to successive steps along the film are obtained by twenty-one slots of logarithmic increments in length, cut in a circular drum 'D'. The drum is only closed at that end near the gearbox 'G\ so that mirror 'M' is actually mounted within the rotating drum. The drum is rotated at a constant speed by a synchronous motor *SM', and via a gear reduction unit 'G\ The electrical supply both to the motor and lamp is through the main switch 'MS'. When this switch is closed the motor and drum rotate continuously but, since the photographic material must only receive an exposure during one revolution of the drum, a shutter *S' is introduced into the light beam. This shutter is driven by a selector mechanism directly connected to a countershaft, running horizontally on a cantilever casting and geared to the main drum. The selector mechanism is arranged to operate as follows: After the main switch has been closed and the drum is rotating, the film is inserted beneath the platen 'PL' and exposing button 'B' is depressed. When the drum has reached a point when the complete area of the film platen is covered, the selector mechanism, which is geared to operate in synchronism with the drum, opens the shutter \S' and, immediately the twentyone step exposures have been made, that is, in less than one revolution of the drum, the mechanism closes shutter 'S' once more and then remains disengaged from the drum, which will continue to rotate, until button 'B' is again depressed. When very slow film is used it is sometimes necessary to allow more than one revolution of the shutter. The roll of film upon which sensitometric exposures are to be made is mounted vertically as shown at *SR' and is taken under platen 'PL' where it is held flat during the exposing period. A typical *2b' strip produced by this instrument is seen in Figure 52 and it should be noticed that a 'V shaped cut has been made in the eleventh step that is, the central one. This locating mark is very useful when plotting curves of densities measured from these strips.