(CJ. II., a 2) The Flap and Drop. This is a combination of
the flap with a drop, and the flap is raised, and then at a given point the drop falls. This class of shutter gives more exposure to the fore-ground than the sky. A modification of this form has been introduced, in which the flap rises, and then turns on a bar and falls like a drop.
(CI. II., a 3) The Double Drop. In this form a sliding piece is raised by pulling a string, and then when the lens is completely uncovered another sliding piece falls, closing the aperture ; thus more exposure is given to the foreground than sky.
(CI. II., a 4) The Rotating Screen. In this style of shutter a rotating screen uncovers and covers the lens aperture. In several shutters of this class a special shape is given to the rotating screen to give more exposure to the foreground.
(CI. II., a 5) The Flap and Double Flap. The principle of this class consists of a flap which is raised and lowered, or one which is raised, opening the lens, and another closing the lens.
(CI. II., a 6) The Go and Return. The disadvantage of this class of shutter is that, if the moving part is heavy and not counterbalanced, the reversal of the motion at the critical moment of exposure, that is, when the lens is fully open, is apt to cause vibration and blurring of the outline. Many shutters of this class are constructed to fit in front of, behind, or between, the lenses.