An exposure aperture frame defining an exposure aperture includes at least a pivotable partition member with an inclined guide surface on the inner wall thereof which is pivoted by and thereby permits advancement of a film leader to a film take-up chamber so that the film leader can reach a film take-up chamber without any standstill within the exposure aperture frame. The inclined guide surface permits the forward end of the film leader to ride across the partition member. A spring urges the partition member toward a position in which it encloses the exposure aperture frame. That spring also releasably retains the partition member on a shaft on which it is pivoted. The partition member has a platform member extending toward the take-up chamber, which has an opening therethrough that provides access to the spring.