FIG. 94.
To make a "Double," attach A to the camera as shown, put B into its place in the opening in A, say on the right-hand side as you stand back of your camera, thus covering up the right-hand side of the plate when exposure is made. Pose your subject on the left hand side, which will give you an image on the right-hand side of your ground glass and plate, draw the slide and expose, immediately returning the slide. This finishes one half of the operation. Shift B over to the left-hand side of A, which will cover up that portion of the plate just exposed, pose your subject again, but on the left-hand side, which will give you the image on the right-hand side of the ground glass and plate, draw the slide and expose out for the exact length of time as at first. On development, if the exposure on both sides has been correct, and of equal length, a perfect negative will be the result.
The camera must on no account be moved between the exposures, nor the focus changed. After making the first exposure the correct focus for the second is obtained by moving the subject backward or forward until an exact focus is secured, and not by moving the camera or ground glass. The whole apparatus should be painted a dead black.
When the attachment is in place it will be noted on the ground glass that while the strip B is just one-half the size of the opening in A, it does not cut off just one-half of the ground glass, a line drawn through the center of which shows that a space in the center of the plate about one-half an inch in width receives a double exposure, but this is not apparent in the finished negative. The figure should be posed as near the center of the plate as possible in each instance. This apparatus, as described, is only available for making two figures. By making B narrower, or one-third of the width of the opening in A, three figures may be made, using each time a separate piece to cover up that portion of the plate exposed, and by changing the form of B to that shown in Fig. 95, four positions can be secured.
FIG. 95.
Val Starnes describes[8] another and still simpler method. He says: Take a light card, mount and carefully cut from it a disc that will fit snugly inside the rim of the hood of your lens, resting against the circular interior shoulder (Fig. 96). Cut from this, in a straight, true line, a small segment (Fig. 97). The exact amount to cut off you can determine by slowly thrusting with one hand a card with a straight edge across the lens hood, looking the while at the ground glass; when the shadow has crept almost to the center of the focusing screen, hold the card firmly in place and notice how much of the circle of the hood is covered by it: cut from your disc a segment corresponding to the amount left uncovered. Don't let the shadow creep quite to the center of the ground glass, for you might go the least bit beyond, and an unexposed strip would result. Now paint your disc a dull black; loosen the hood of your lens on its threads, so that it will revolve easily and freely, and you are ready for business.
[8] "American Annual for 1895."
FIG. 96. and FIG 97.