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July 1947 HIGH-SPEED UNDERWRITER PHOTOGRAPHY 71
similar troubles, and thus would increase the possibility of obtaining successful records from all cameras.
The main requirements for the film drive have already been in dicated, i.e., smooth acceleration and deceleration to prevent damage to the film. However, the fact that this film was to be used for precise measurements made it desirable to maintain a constant film speed during the exposure and also a fixed relationship between the film speed and the number of flashes. This latter requirement is, of course, equivalent to the specification of a constant frame size, and, if it can be made to work satisfactorily, it offers a possibility for the development of a relatively simple projector to present the record in the form of ultra-slow-motion movement.
Since these cameras are to be used as measuring instruments, they must be as carefully aligned and as permanently fixed to the windows of the tank as would be necessary for the use of any other optical measuring instrument. This means that the magazines must be of the daylight-loading type since the cameras cannot readily be removed from the tank and taken into the darkroom for reloading. Obviously, if a daylight-loading type of magazine is to be used, each strip of film will contain a small exposed portion which can also be made to contain the splice. To obtain a complete record of the experiment, measurements must be started at the beginning of the entire unexposed length of film, or, in other words, just after the exposed portion, including the splice, has passed through the camera. If this condition is to hold simultaneously for all of the cameras in the battery, then the lengths of the film in all of the magazines must be identical ; i.e., they must have the same number of sprocket holes per film belt. If this condition can be otained, then all of the splices in the exposed portions of the film can be set at the same relative position and will maintain this relation during the entire run.
To secure identical lengths of film in each magazine requires a precision-loading technique, a prerequisite of which is an exact means for measuring the film being loaded. Furthermore, an endless-belt type of magazine demands a fixed predetermined pattern of threading which must be maintained during the loading and unloading cycles. The best way of meeting these rather complicated demands appears to be through the construction of a magazine loader which would incorporate a film-measuring device, a splicer, and film supply and take-up rolls of sufficient size to load the entire camera battery a number of times. Since this auxiliary piece of equipment is necessary