Cl. II., c) Shutters Working Between the Lenses, This variety is again divided into (i) The go and return ; (2) the
blind or drop ; (3) opening from and closing to centre with eyelid aperture ; (4) opening from and closing to centre with diamond aperture; (5) opening from and closing to centre with longi-tudinal strip opening; (6) Iris dia-phragm action : (7) rotating screen.
(Cl. II., c \) The Go and Return. This form has for some time held the front rank in between-lens shutters, but is open to the theoretical objection that the reversal of the motion at the critical moment of exposure, when the lens is fully open, is liable to cause vibration.
(Cl. II., c 2) The Blind or Drop. In the case of the drop it is obvious that the lens mount has to be cut to allow the dropping-piece to pass through. This has, probably for this reason, found but little favour. The blind form is practically the same as that made for the front of the lens but with a narrow slit.
(Cl. II., c 3) Opening from and Closing to the Centre with Eyelid Aperture. This form of aperture is a favourite one.
(Cl. II., c 4) Opening from and Closing to the Centre with Diamond Aperture.
(Cl. II., c 5) Opening from and Closing to the Centre with Longitudinal Strip Opening. So far as I am aware there is only one commercial shutter which gives this form of opening, and it consists of double blinds which work in opposite directions. (Cl. II., c 6) Opening from and Closing to the Centre with