Traditionally strips of film have been wound into a light tight cartridge with a film leader portion sticking out to facilitate either manual or automatic loading onto a take up spool. Activation of the camera's picture taking mechanism in some cameras has been delayed by first sensing the existence of the film's leader portion which is designed with a width that is less than the width of the film strip. The delay being maintained until the camera detected a transition between the narrow leader portion and the wider film portion of the film strip. One prior art arrangement used different sized indicia in the leader portion than in the film portion of the film strip. Activation of the camera's picture taking was delayed until a size change in indicia was noted indicating that the film had been properly loaded and advanced. Another type of film cartridge, not presently in wide spread use, does not require the use of a take up spool or operator intervention to advance the film from the cartridge. With this type of cartridge the film strip is thrust out along a film path when the film cartridge is inserted in the camera. A notch is provided at the beginning of the leader portion 16 as shown in FIG. 1 as 22. That notch 22 is on the same side of the film strip 14 as the indicia 24A and 24B. The dimensions of the notch 22 and indicia 24A and 24B are such that it is not possible to distinguish between the two using a standard optical sensor arrangement. One simple method that has been tried is to set a time delay after the leader portion of the film has been detected. During the delay, the optical sensor is turned "off" so that a false signal from the notch will not be detected. After the delay, the optical sensor is turned back "on" again and monitoring for the first anticipation perforation begins. The problem with this method is that film travel, on thrust, may vary greatly due to external conditions such as individual cartridge characteristics, interference with a magnetic head (for those cameras that utilize film having magnetic strips or other indicia), temperature, battery conditions, etc. Therefore, setting an appropriate delay may not always be reliable. As a result some other means of either detecting or ignoring the notch is necessary. The present invention directs itself to an apparatus for solving this problem.