. Transactions of the Society of Motion Picture Engineers (1921) . scale impressed by intermittent exposure is easily obtained with asector wheel having a series of angular openings of the followingvalues : 180 - 90 - 45 - - - - - and .703 de-grees. Each angular openings passes twice as much light as the pre-ceding one and gives double the exposure. The sector wheel is re-volved during the exposure in front of and as near as possible to thesensitive film. For negative emulsions it is usual to expose 40 140 and as the largest angle on the wheel is 180° we mus
. Transactions of the Society of Motion Picture Engineers (1921) . scale impressed by intermittent exposure is easily obtained with asector wheel having a series of angular openings of the followingvalues : 180 - 90 - 45 - - - - - and .703 de-grees. Each angular openings passes twice as much light as the pre-ceding one and gives double the exposure. The sector wheel is re-volved during the exposure in front of and as near as possible to thesensitive film. For negative emulsions it is usual to expose 40 140 and as the largest angle on the wheel is 180° we must give an ex-posure of to obtain an effective 40 The form of thewheel is shown in Fig 3. When the exposures are made with awheel of this type there is a constant error known as the inter-mittency error. If an emulsion is given, for instance, a continuousexposure of one second, and upon development yields a certaindensity, another strip of the same emulsion which has been given aseries of intermittent flashes which altogether total one second will,. Fig. 3—Sector Wheel of Sensitometer. Upon development, give very much less density than the one whichreceived the continuous exposure. The continuous exposure broughtabout a definite light change in the silver bromide emulsion, the in-termittent exposure coming in flashes, each flash made very littleeffect upon the emulsion and there is a tendency for the slightlyacted upon silver halide to return to the normal or stable condition,hence the intermittency error is most noticeable through the smallangles of the wheel and is least objectionable when measuring veryfast emulsions. The error, however, becomes very great on slowemulsions and would be altogther too high for reliable readings ofpositive film.
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