A lens system (400b; 500b) having a stacked structure and comprising at least: a first lens (410; 510); a second lens (420; 520) adjacent to the first lens (410; 510), a first space formed between the second lens (420; 520) and the first lens (410; 510); and a shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820) between the first lens (410; 510) and the second lens (420; 520), the shim(430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820) having at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822), the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) connecting the first space and a second space outside the first space wherein: the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820) has a first contact surface with the first lens (410; 510) and a second contact surface with the second lens (420; 520), the first contact surface and the second contact surface forming an overlap area on the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820); the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) extends across the overlap area on the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820); characterised in that the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) has a radial width greater than a radial width of the overlap area; and the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) has a radial width less than a radial width of the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820). a first lens (410; 510); a second lens (420; 520) adjacent to the first lens (410; 510), a first space formed between the second lens (420; 520) and the first lens (410; 510); and a shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820) between the first lens (410; 510) and the second lens (420; 520), the shim(430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820) having at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822), the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) connecting the first space and a second space outside the first space wherein: the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820) has a first contact surface with the first lens (410; 510) and a second contact surface with the second lens (420; 520), the first contact surface and the second contact surface forming an overlap area on the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820); the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) extends across the overlap area on the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820); characterised in that the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) has a radial width greater than a radial width of the overlap area; and the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) has a radial width less than a radial width of the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820). the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820) has a first contact surface with the first lens (410; 510) and a second contact surface with the second lens (420; 520), the first contact surface and the second contact surface forming an overlap area on the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820); the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) extends across the overlap area on the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820); characterised in that the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) has a radial width greater than a radial width of the overlap area; and the at least one venting hole (432; 570; 612, 622, 632, 642, 652, 662; 712, 722; 812 822) has a radial width less than a radial width of the shim (430; 530; 610, 620, 630, 640, 650, 660; 710, 720; 810, 820).