An adapter, comprising: an adapter body, wherein the adapter body is hollow; an interface matched and connected with a photographic accessory is arranged on a first side of the adapter body; a rotating ring rotatably connected to a second side of the adapter body; at least three sliding connecting pieces; wherein the rotating ring comprises rotating ring guide grooves; each sliding connecting piece is corresponding to at least two rotating ring guide grooves; the adapter body comprises adapter body guide grooves; each sliding connecting piece is corresponding to at least two adapter body guide grooves; each rotating ring guide groove is corresponding to each adapter body guide grooves; each sliding connecting piece is fixedly connected to corresponding at least two guide elements; each of the guide elements passes through a corresponding rotating ring guide groove to slidably connect to a corresponding adapter body guide groove; each sliding connecting piece is slidably connected to corresponding at least two rotating ring guide grooves and corresponding at least two adapter body guide grooves by corresponding at least two guide elements passing through the corresponding at least two rotating ring guide grooves; so each sliding connecting piece moves along the corresponding at least two rotating ring guide grooves and the corresponding at least two adapter body guide grooves when the rotating ring rotates with respect to the adapter body; wherein the at least two guide elements corresponding to each sliding connecting piece are in one-to-one correspondence with the at least two rotating ring guide grooves corresponding to each sliding connecting piece and are in one-to-one correspondence with the at least two adapter body guide grooves corresponding to each sliding connecting piece; wherein each sliding connecting piece comprises a connecting portion when each sliding connecting piece moves along the corresponding at least two rotating ring guide grooves and the corresponding at least two adapter body guide grooves, configuration of the corresponding at least two rotating ring guide grooves and configuration of the corresponding at least two adapter body guide grooves of each sliding connecting piece make the connecting portions of the at least three sliding connecting pieces to form a circumferential distribution; a diameter of the circumferential distribution formed by the connecting portions increases or reduces along with movement of the connecting portions to fit a camera lens. an adapter body, wherein the adapter body is hollow; an interface matched and connected with a photographic accessory is arranged on a first side of the adapter body; a rotating ring rotatably connected to a second side of the adapter body; at least three sliding connecting pieces; wherein the rotating ring comprises rotating ring guide grooves; each sliding connecting piece is corresponding to at least two rotating ring guide grooves; the adapter body comprises adapter body guide grooves; each sliding connecting piece is corresponding to at least two adapter body guide grooves; each rotating ring guide groove is corresponding to each adapter body guide grooves; each sliding connecting piece is fixedly connected to corresponding at least two guide elements; each of the guide elements passes through a corresponding rotating ring guide groove to slidably connect to a corresponding adapter body guide groove; each sliding connecting piece is slidably connected to corresponding at least two rotating ring guide grooves and corresponding at least two adapter body guide grooves by corresponding at least two guide elements passing through the corresponding at least two rotating ring guide grooves; so each sliding connecting piece moves along the corresponding at least two rotating ring guide grooves and the corresponding at least two adapter body guide grooves when the rotating ring rotates with respect to the adapter body; wherein the at least two guide elements corresponding to each sliding connecting piece are in one-to-one correspondence with the at least two rotating ring guide grooves corresponding to each sliding connecting piece and are in one-to-one correspondence with the at least two adapter body guide grooves corresponding to each sliding connecting piece; wherein each sliding connecting piece comprises a connecting portion when each sliding connecting piece moves along the corresponding at least two rotating ring guide grooves and the corresponding at least two adapter body guide grooves, configuration of the corresponding at least two rotating ring guide grooves and configuration of the corresponding at least two adapter body guide grooves of each sliding connecting piece make the connecting portions of the at least three sliding connecting pieces to form a circumferential distribution; a diameter of the circumferential distribution formed by the connecting portions increases or reduces along with movement of the connecting portions to fit a camera lens.