Exposure in the Camera.[J]
[J] Remarks as to the selection of the view, &c., are not given, as this can be effected by the individual taste of the operator, but care must be taken that direct rays from the sun shall not fall on the lens or enter the camera during the exposure of a plate.
As has been before stated, this operation may take place immediately the plate is thoroughly dry after being excited, or a fortnight may intervene between the excitement and exposure, provided the plate is kept very carefully excluded from light and any chemical or sulphurous vapors, in a plate-box adapted for that purpose, with the sensitive surface towards the back of the box. When the exposure is about to take place, or at any time previously, the camera-backs may each have a plate placed in them ready for exposure; to do this, the camera-back must be taken into the operating room and the door closed, so as to exclude all white light. The hinged flap of the camera back is opened, and the prepared plate laid, with its sensitive surface downwards, or next the sliding flap, so that its corners may rest on the silver wire corners of the plate frame previously placed within the camera back ready to receive it. The hinged flap is now closed and kept from opening by turning the flap button over it; the sliding flap is examined to see that it is pushed closely down so as to guard any access of light, and it is then ready to be placed in the camera, and may be taken into the open air with impunity. Should the exposure not take place immediately, or, should the camera back have to be carried any distance, it is advisable either to wrap it up in black cloth, or secure the flaps from the chance of coming open during transit, by a stout string being tied around the back.
The focussing is conducted in the usual way and the cap replaced on the lens; the focussing glass is now removed and the camera back fitted into the same aperture, with the sliding flap next the lens. The sliding flap is pulled up to its fullest extent, placing the hand on the camera back to prevent it rising out of the camera with this action. The cap of the lens is then removed, so that the light may be admitted into the camera, and to fall on the sensitive surface of the plate. After the necessary time of exposure has taken place, the cap is replaced on the lens, the sliding flap is pushed down, and the camera back withdrawn from the camera; the plate can then be taken into the operating room to be developed, or this operation may be deferred for days or even a week, or more if convenient. The time of exposure in the camera varies according to the intensity of the light and the aperture and focal length of the lens; therefore, to give the exact time of exposure would be impossible, still it may assist the amateur if I give the time required in summer with full sunshine, and merely state that this time may be increased to double in winter or dull weather.
In the ordinary sunshine of a summer's day the time of exposure will be:
30 seconds with a lens of 4-inch focus and ½-inch stop.
21 seconds with a lens of 4-inch focus and 5/8-inch stop.
5 seconds with a lens of 4-inch focus and 1¼ inch aperture with no stop.
1½ minute with a lens of 6-inch focus and ½-inch stop.
4½ seconds with a lens of 6-inch focus and 2¼-inch aperture with no stop.
2 minutes with a lens of 8-inch focus and ½-inch stop.
1¼ minute with a lens of 8-inch focus and 5/8-inch stop.
3¼ minutes with a lens of 10-inch focus and ½-inch stop.
2 minutes with a lens of 10-inch focus and 5/8-inch stop.
5 seconds with a lens of 10-inch focus, 3¼-inch aperture, with no stop.
6¼ minutes with a lens of 14-inch focus and ½-inch stop.
4 minutes with a lens of 14-inch focus and 5/8-inch stop.
2¼ minutes with a lens of 14-inch focus and ¾-inch stop.
8¼ minutes with a lens of 16-inch focus and ½-inch stop.
5¼ minutes with a lens of 16-inch focus and 5/8-inch stop.
2¼ minutes with a lens of 16-inch focus and ¾-inch stop.
Developing the Image.
The camera back is taken into the operating room, from which all white light is carefully excluded, the plate removed from the camera back, and laid, albumen side upwards, on the fixing stand; as much distilled water is now poured on it as the surface will hold, taking care that every part of the sensitive surface is covered with the liquid; allow the water to remain on the surface for one minute, then pour off and drain slightly; replace the plate on the stand, and pour over the surface so as thoroughly to cover every part, the pyrogallic solution (made as described at [page 192], and carefully filtered just before being used); allow this to remain on the plate for one minute, then drain off into a perfectly clean measure, and add to it an equal bulk of silver developing solution, [page 192]; mix these thoroughly together with a glass rod, and then pour the mixed liquids over the plate; allow them to rest until the picture begins to appear, which generally takes about from three to five minutes; then pour off and on repeatedly, until the developing fluid becomes opaque, which then contains floating particles, and these, if allowed to do so, would settle on the plate, to the injury of the picture; but this may be prevented by brushing the surface with a camel's-hair brush frequently during the development. When this opacity of the developing fluid takes place, drain all the fluid off the plate, and thoroughly wash with water; then mix another quantity of pyrogallic and silver developing solution in the same proportions as before, and pour this on and off the plate as before, until the picture appears sufficiently intense, and the middle shades well brought out; when this takes place drain off, and wash with water, so as to clean the surface thoroughly, and the plate is then ready for the next step, "fixing the image."
Should the picture begin to develope in less than three minutes after the application of the mixed developing fluids, thoroughly drain the plate, and wash well with water, then continue the development with a solution of three parts pyrogallic solution and one part silver developing solution; but should the picture not begin to appear in five minutes, the addition of half a drachm of the albumen bath solution to each ounce of mixed developing solution will be necessary, in order to obtain the middle shades and the required intensity. It may be stated, as a guide, that the best negatives which the author has produced occupied from ten to twelve minutes in developing.
Fixing the Image.