A person shall not be guilty of a violation under this chapter if he is a librarian, or a paid or volunteer member of a library staff working under the supervision of a librarian, engaged in the normal course of his employment, or if he is regularly employed by anybody as a motion picture projectionist, stage employee or spotlight operator, cashier, doorman, usher, candy stand attendant, porter or in any other nonmanagerial or nonsupervisory capacity in a motion picture theatre; provided that he has no financial interest, other than his employment, which employment does not encompass compensation based upon any proportion of the gross receipts, in the promotion of a sexual performance for sale, rental or exhibition or in the promotion, presentation or direction of any sexual performance, and provided further that he is not in any way responsible for acquiring such material for sale, rental or exhibition.