I acquired a Minolta Autopak-8 S6 for $10 and picked up a pack of TRI-X B/W outdoor film. I figured I'd do some lighting test shots with it and have run through the alotted 50' according to the gauge on the side of the camera. How do I know when it hit s the end...There was a slight pace change in the whirring that happend a bit after 50'...is that the I'm done sound?