Home >> Photography Theory And Practice >> An Outline Of Cinematography to Focal Length Of Lenses >> Darr Room Accessories 262_P1

Darr-Room Accessories 262

films, plates, tank, film, tanks, liquid, time and roll

Page: 1 2 3 4

DARR-ROOM ACCESSORIES 262. Tanks and Dishes. If only one or a very few negatives are treated at a time, the plates or cut films may be laid flat in a shallow dish, but when large numbers are often treated at once much time is saved if they are placed in a deep tank holding several plates vertically.

Dishes are made with the sides splayed out wards,' and with a lip at one of the corners for pouring the liquid out. The dishes most fre quently used are not deep enough, especially in large sizes ; the depth being usually the same for a dish 2o X 24 in. as for one 5 X 4 in.

For many years it was usual to make project ing ridges on the inside of the bottom of the dish to facilitate the removal of the plates. This practice was a nuisance in the use of papers and is now almost entirely abandoned. In its place we have a shallow channel along the two long sides of the dish, which allows of the intro duction of a finger nail or a hook under the plate to lift it.

Tanks for vertical development have for a long time been made with grooves in the two opposite sides, or carrying a movable frame work fitted with grooves. One plate is inserted in each pair of slots or sometimes two back to back. The removal of the plates by their edges is not always easy, and the grooves are often very close together, thus reducing the quantity of liquid in contact with the sensitive film under treatment. These types of vessels, moreover, cannot be used for cut films.

A developing tank invented for the use of the French Military Aviation (E. Cousin, 1914) was a marked improvement on vessels for ver tical development then known ; it was adopted afterwards by the various allied armies, and its use has spread in all branches of photography, either in its original form for plates, or, after certain modifications, for cut films.

The plates or films are placed singly in metal frames or hangers' (Fig. 161), where plates are held during all the operations until drying, or even including drying, in the case of films. The frames, once filled, are introduced one by one, 2 and left for the time necessary in the different baths and in the washing tank. Hangers are supported by their crosspieces on the top edge of the tank or on an internal ledge (Fig. r6o), the latter arrangement facilitating the fitting of a light-tight lid, which enables white light to be turned on in the dark-room during development, if need be.

The tanks should always be of such size that the plates are covered by at least in. of liquid and allow in. of liquid below them, for the accumulation of used developer or the deposition of sediment and insoluble matter.

The capacity of these vertical tanks is con siderable (about 3 gallons for 12 X 10 in.), and

it would be ridiculous to pour the by no means exhausted developer into a bottle every time it is used, to protect it from spontaneous oxidation. A very ingenious way of protecting the developer consists in placing in the tank, when not being used, a floating lid (shown in position on the tank in Fig. 159). This lid fits in the vessel with as little play as possible, thus reducing the surface of liquid in contact with the It is easy in a given tank to treat plates or films of any size smaller than those provided for. Hangers for plates 7 x 5 in. upright can be used for plates 5 X 4 in. on their sides. Also, movable crosspieces may be fitted on which to rest frames smaller than those intended., 263. Special Tanks for Roll Films. A descrip tion of all the methods for development of roll films would carry us too far afield. For the amateur's roll film we have tanks into which the film may be introduced in daylight, no dark-room being required. For cinematograph films we have frames immersed in a large vessel, or horizontal drums, with the film wound on them, revolving on an axis. The lower part only is immersed in the bath, and the steady rotation ensures uniform action on the film. Different types of apparatus for the treatment of the amateur's spools singly will be found in any catalogue of photographic apparatus ; for equipment of the cinematograph dark-room we must refer the reader to special works.' The commercial processing of roll films (developing and printing) for the amateur is generally done in deep tanks, the films being held by clips hung on a rod, by single hangers, or by racks holding several films. Long films are often fastened at both ends by the same clip, the two sides being held apart by a cylin drical roller weight or by a cross-piece of the For long strips of film used in automatic cameras for aerial photography, viz, films too large to be handled on frames similar to those used in cinematography, the only practical apparatus is, to our knowledge, the large-scale model of the Kodak cylindrical tank, made for development of roll films in daylight (Eastman Kodak Co., 1918). The film to be developed is wound on a suitable spool with a sheet of cellu loid provided on its two edges with toothed rubber bands, which keep the coils of the film from one another, permitting the access of the liquid and the escape of air when the successive solutions are poured into the cylindrical tank holding the spool (the model made for the U.S. Air Service takes films 25 yd. long and about 7 in. wide).

Page: 1 2 3 4