Various devices have been employed to enable an instantaneous shutter to give a longer exposure to the foreground than to the sky. Most of them, however, are mora or less complicated and expensive, and nearly all the devices with which the writer is acquainted are patented. The shutter which forms the subject of Fig. 236 is free from all the above objections. It is the invention of Mr. Jarvis, a Chicngo amateur, is extremely simple in construction and Button, easily made by any one with any "tinkering" propensities, and is very light and compact. As shown in the sketch, it consists of a vertical slide working in a frame in the usual manner, the frame being provided with a stop at the bottom to arrest the slide at the lowest or "closed" position. The back of the frame is solid, except where cut out to fit lens mount, as shown by dotted circle. The front is open, being merely provided with guide strips for the edges of slide. This slide must be mode of some light material -wood or ebonite being preferable. A small screw-eye is inserted at d, while a pin, slightly bent downwards, is put in at c. A robber band a is hooked under the latter, while another one b, is pissed through the former. Both these bands are screwed by their ends to the sides of the frame by screws as shown.
The band a should bo just "taut" when horizontal; b must be a little slack when the shutter is closed. The full lines in the sketch show both bands in the position they occupy when the shutter is at its lowest position, while the dotted lines show them at its highest point. A trigger is provided for releasing the shutter, but it was not considered necessary to show that, as there is nothing peculiar about it; a pneumatic attachment can be used if preferred. The action of the abutter is as follows: - The slide being in its lowest position, is held in place by the trigger, while the band a is hooked under pin c. On releasing the trigger, this rubber band causes the slide to fly up, sod gives it sufficient impetus to carry it for beyond the travel of the band itself; this impetus is exhausted in stretching the band b, and, in recoiling, this latter drives the shatter "home" again. As the band a is, when released, somewhat in front of the end of pin c (see side view), the Utter does not touch it in its descent. (P. H. Davies.)
With the introduction of bromo-argentic gelatine paper for copying and printing purposes, improved devices have been required for making short and rapid exposures. Several plans suggested themselves, but the one which is herewith described was that which was adopted as being both rapid and simple. On working a large number of gelatine prints, it was important that there should be no delay, as might be occasioned by the necessity of opening the dark-room door for the purpose of making exposures to actinic light. This device is constructed to avoid the difficulty, and with it exposures can be made while the development of other pictures is going on in the dark room.
Fig. 337 represents a side elevation; Fig. 238, a front elevation; Fig. 239, the device adapted for use by artificial light.
b is a permanent wood frame set obliquely in, and forming part of, the non-actinic light sash frame, which is set just behind the outer sash.
a is a cotton blind or curtain of double thickness, painted a non-actinic colour - such as a deep orange ruby, or it may be black - which is open at the bottom, having its ends secured by narrow strips (as shown in Fig. 238) to an ordinary spring roller; c d is a metal wire guide which holds the curtain light-tight against the frame b. The top of the curtain is kept flat and straight by the usual blind stick.
A cord e, secured by a screw-eye to the blind stick, runs up over a pulley, through a hole in the sash frame to the inside of the dark room. A knot made in the cord at the right point prevents the curtain from going down too tar, and holds it in the position shown in Fig. S3T.
The operation is simple, the printing frame being inserted in the frame A, making a close fit, as shown in Fig. 237, the glass tide being towards curtain a.
The cord e is pulled down quickly in the dark room, which bring* the open portion of the blind a in front of the frame, exposing the latter to aclinic light, which enters through the outer sash. Upon releasing the cord e, the spring roller o end the force of gravity pull the blind a rapidly back. The exposure can be made in a second, and sometimes shorter.
On Fig. 239 is shown the tame construction, except that in place of diffused daylight is substituted an oil lamp, between which and the blind is located a sheet of ground glass f. Such an arrangement is useful in making transparencies at night, as the same light will partially light the dark room and furnish light for the exposures. Different tiled kits may be made to fit the frame b, and thus accommodate different printing frames.
A table or shelf is conveniently arranged in front of the window, which permits the printing frame to be easily handled. The device has been in practical use for a long period of time, and has never become deranged. Its efficiency has been proved. (F. C. Beach).
The amateur photographer in the early stages of his career has perhaps spoiled a large percentage of his plates by fogging - sometimes due to carelessness, but mora frequently to a want of knowledge regarding the capabilities of his apparatus.
The camera, with the plate holder attached, is presumed to be light-tight, but very often is not. The 2 weak points are the sliding front and the junction of the holder with the camera. By holding it up to direct sunlight, and alternately looking in from front and rear, any defect will be detected.