With this shutter, the latest production of the inventor of the very popular "Eclipse" shutter, exposures can be made of any desired duration. It is equal to any requirement for the most rapid work, and as a time shutter, exposures can be made as quick as two pulsations can be given to air bulb (about one-tenth of a second) or of minutes' duration.

"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.

Prosch s Duplex Photographic Shutter For Timed Or  PhotographyInStudioAndField 63

The illustration gives a front view of the shutter, one-half size of No. 2, which is suitable for an 8x10 lens, or even larger, as it has an opening at the diaphragm of 1 1/8 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 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.