"Duplex" Shutters work perfectly, with even the very largest lenses, up to their full capacity; and several lenses can be used with the same shutter. The shutter gives a full opening; but yet, by the peculiar opening in the exposure slides, any part of the picture can be favored with more or less illumination by turning the shutter, sometimes even inverting it.
The illustration gives a front view of the shutter, one-half size of No. 2, which is suitable for an 8×10 lens, or even larger, as it has an opening at the diaphragm of 11⁄8 inches.
Inclosed in metal casing are two pivoted slides, which move, in unison, in opposite directions, and make the exposure in one continuous movement without the slightest jar, even when worked at its greatest rapidity. The motive spring is on the back of the shutter, and is of coiled wire; a perfectly reliable spring. Its tension is regulated by moving it along a series of notches. The exposure slides are moved by a stud on the lever shown on front, which passes through the shutter and a slot in each slide, and engages with the spring on the back. On the end of the lever are two notches hidden by the secondary lever. When the lever is fully depressed, the release catches in the upper notch and locks the slides closed. A slight pressure on the air bulb or a trip to the projecting end of the release, frees the slides, and they make an instantaneous movement or exposure. If the secondary lever has been brought into play, by a turn or p130 two of a milled-head nut, the release will catch in the second or lower notch and hold the slides at a full opening, in which position they remain until a second pressure is given to the bulb, or the release is tripped by hand.
The shutters are made in standard sizes, having narrow threaded collars on each side, to which can be adapted tubes to receive lenses, which are to be transferred from regular lens tubes. Any intelligent instrument maker or machinist can adapt such tubes to lenses; the original tube is not used.
HEAD-RESTS.
It might have been thought that the rapid dry plate, by shortening the time of exposure so much, would have done away with the necessity for using head-rests; and many old photographers whose backs have often ached from handling the "Wilson," the "Spencer" and other enormously heavy head-rests, thanked their stars that a time of relief seemed to be at hand. But not so. The head-rest is just as necessary as ever, and the heavy ones are as advantageous now as before. The most important use of the head-rest is to keep the head in the position required. That the head should be immovable is necessary during the time of exposure. Many people are quite able to keep still enough for photographic purposes without a rest for the head, but very few are able to keep the head in the position desired by the operator without some assistance; hence the necessity for the use of the head-rest for even the shortest exposure. One benefit, however, has been derived from the advent of short exposures; there seems no necessity for the use of the extremely heavy varieties. p131 The lighter rests would seem to be capable of fulfilling all the requirements of a head-rest.
[SUCCESS HEAD-REST.]
CENTENNIAL HEAD-REST.