DOUBLE EXPOSURES Two exposures may be made on one plate— each one filling half the plate—by having a shield of metal or thin wood fitted to the camera back dose to the dark slide. The shield covers half of the plate while the other half is exposed ; then the position of the shield is changed so that for the next exposure it covers the exposed half while the second half is exposed. The shutter of the slide may be drawn right out for each exposure ; the shield forms a perfect pro tection for the part covered. By means of such a fitting a half-plate may be used for two quarter plate exposures.
A few years ago this method of making two exposures on one plate was very frequently used by amateur photographers for producing a type of portrait that could not be attained by any other method excepting combination printing. (See " Doubles.") Another form of double exposure is that which is frequently utilised for obtaining " spirit " or " ghost " photographs.
A plate is exposed in the usual manner on the subject in which it is intended that the " ghost " should appear. The lens is capped while the figure that is to form the ghost is introduced. Then a short supplementary exposure is made, care being taken to avoid moving any part of the subject between the two exposures. A transparent shadowy image of the added figure will appear, solid objects in the picture being visible through it.
An annoying form of double exposure is that obtained by exposing the same plate twice, by accident. The best method of avoiding this is to make it a rule to change the plate immediately after exposure when using a magazine hand camera, and to expose all plates in rotation according to the number on the dark-slides when these are employed.