which consists of two pieces of wood, each having a hole cut into
it, and so arranged that when one piece is placed upon the end or
hood of the lens (which fits into the circular opening), the other
piece can be made to slide up and down against it, thus for an
instant bringing the two openings opposite, and making the exposure
depend upon the rapidity with which one opening passes the other.
[Illustration: FIG. 1.]
[Illustration: FIG. 2.]
Fig. 1 represents the common form, in which the release is made by
the withdrawal of a metal catch, which fits the indent in the side
of the sliding upright piece. Fig. 2 represents an improved form, in
which the release is made by pressing a rubber bulb connected with a
rubber tube attached to a metal valve.
The action of both these styles of drop shutter may be hastened by
using rubber [p165] bands to quicken the fall of the sliding
piece, as represented in Fig. 2 by A and B. So that while a rapid
exposure might be made by the fall of the slide, by its own weight,
it would not be quick enough for an object moving across the plane
of focus, but might be sufficient for an object moving away from or
toward the lens. By the use of the rubber bands the exposure may be
made as quick as a flash, or the small fraction of a second, thus
enabling one to secure a sharp impression of the trotting horse, the
railroad train, the racing yacht, and many other interesting and
difficult subjects.
Another peculiarly effective form of shutter is that known as THE
PROSCH ECLIPSE SHUTTER, which is a small and compact instrument,
made of metal and rubber, by which an exposure of 1/200 part of a
second may be made, with the power of reducing the speed to about
one-half second.
[Illustration: THE PROSCH ECLIPSE SHUTTER] [p166]
A late and decided improvement on the Eclipse Shutter has been
produced by Mr. Prosch, which he has named the "Duplex."
[Illustration: TN: Prosch's Duplex Shutter.]
Prosch's Duplex Shutter is intended both for "timed" and
instantaneous exposures.
It is equal to any requirement for the most rapid work, and as a
time shutter, exposures can be made of from one-half second to any
duration required.
The peculiarity of this shutter is that the exposing slides are
placed between the front and back combinations of the lens,
necessitating a separation of the tube at the centre. [p167]
Mr. Prosch makes a special tube to which is affixed the apparatus of
the shutter. This special tube is of the exact size of that to which
the lenses belong, from which the lenses are taken and fitted to the
special tube. The other is kept for future use if necessary.