the film if the film scrap is carried off the film path by the clip large forces may be generated between the film and clip that make film removal by a jet of fluid difficult frequently there is an oven enclosure 61 shown in dashed lines surrounding a major portion of the stretcher 23 for heating the film as it is being stretched there are a plurality of sensors such as sensor 63 located in the oven and directed at the film to monitor film temperature for control purposes in the case of film tears the temperature sensed by the sensor 63 changes dramatically as the film moves away from the sensor and this can be used to detect film tears in the stretcher in this case the sensor 63 also serves as a position detector to sense the presence of the planar film in the stretcher a controller 65 is used to operate the stretcher and monitor the output from sensors such as sensor 63 fig2 shows view 2 2 from fig1 that is an end view of a clip carriage 64 supported by track section 66 mounted to frame 67 the clip carriage 64 comprises a track engaging portion 68.