This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
549. Ever since portraiture by means of photography was seriously considered, the professional, as well as the manufacturer of photographic apparatus, has been constantly experimenting and trying to secure some satisfactory method of artificial lighting. Flashlight photography has for many years been employed, but it has many drawbacks, chief of which are the inability to focus with this light, the danger in using it, and the variation in exposure if not handled with most extreme care. Electricity has been used to a considerable extent, but not until the introduction of the Aristo Electric Lamp, has a sufficient amount of actinic rays of light been at the command of the photographer to permit of giving a reasonably short exposure - exposures equally as short as those required under the ordinary skylight.
550. The following description of the Aristo Lamp tells, in a practical way, the advantages of the lamp, as well as its construction and application to portraiture. In order to establish a long arc and regulate it to obtain sufficient actinic rays to effect the sensitive plate quickly, it is necessary that the controlling mechanism which separates and feeds the carbons should have special features not ordinarily found in arc lamps. With a short arc the light emitted from the carbons is white and, therefore, particularly adapted for illuminating purposes. With increasing lengths of arc, the light has a larger proportion of violet rays and is best suited for photographic printing purposes. The Aristo arc lamp has been specially designed with this point in view.
551. The current enters the lamp at the positive binding post, passes through a flexible connection into the upper carbon, through the arc, the lower carbon, the lifting magnets, and then through the rheostat to the negative binding post. The regulating magnet is so proportioned as to keep the carbons a long distance apart and keep the current constant for the various positions that the armature assumes. The rheostat is so designed that the voltage which is consumed in it can be regulated, so the lamp can be readily adapted for various terminal pressures.
Illustration No. 71. Construction of Aristo Lamp.
See Paragraph No. 554.
552. For all direct current lamps an ohmic resistance is used, while for alternating current lamps an inductive resistance is used, which latter has the advantage that it does not consume as large amount of energy as does an ohmic resistance. The amount of energy consumed in an inductive resistance is represented by the iron and copper losses.
553. The connection of the lower carbon holder to the side rod supporting it is so designed that the return current in the side rod can not exert a disturbing effect upon the arc. The globe is held to the lamp by means of a spring bail allowing free expansion of the glass.
554. 110 volt direct current arc lamps consume approximately 28 amperes, while 220 volt direct current lamps consume approximately 14 amperes. On alternating current, Aristo Lamps are used on all commercial frequencies. The 110 volt alternating current Aristo Lamps are adjusted for 28 amperes, while the 220 volt alternating lamps are adjusted for 14 amperes. The 220 volt direct and alternating current lamps operate with an arc voltage of about 150 volts. (See Illustration No. 71.)
555. The advent of the Aristo Lamp into photographic studios opened a new era of progress for the photographer. Without a lamp of this kind, he was largely, if not entirely, dependent on the rays of the sun as the only means for operating and printing. Dark weather meant poor business, and unfortunately, during the holiday season, when the demand for work was greatest, the most unfavorable weather conditions prevailed. A month of cloudy skies before Christmas cut out the profits of the year. The delivery of work was a mere speculation and has always been a source of disappointment to the customers.
556. With an Aristo Lamp in the studio, these conditions are all changed. The operating room can be flooded with a beautiful violet-tinted light day or night. This violet light has the same actinic properties as bright sunlight, and therefore, will make photographic prints or negatives in the same time. Skylights being unnecessary, the operating room can be located on the ground floor in any building, thus enabling the photographer to locate at a point more advantageous to his trade than if he were obliged to use a skylight.
557. As the lamp may be hung in any part of the room, the operator has absolute control of the direction of the light, and consequently should be able to obtain any lighting he desired.And as the light is always of the same strength he can always be certain that the exposure is correct. Work can be promised for a certain date with absolute confidence that it will be ready.
558. The simplest method of using the lamp for operating is to diffuse the light through a screen of muslin placed between the light and the sitter, the softness of the lighting depending on the distance of the screen from the lamp. A more practical way is to inclose the lamp in a hood.
559. There are several ways of using the hood, all of which are more or less modifications of the one here illustrated and explained. (See Illustration No. 72.) This hood is a triangular effect, except that the front is twelve inches wider than the sides. The front measures forty inches high by fifty-two inches wide. This is covered with tracing cloth. The sides, which are forty inches wide by forty inches high, are covered with white material; the bottom is also covered with the same material. An additional thickness of opaque black muslin is placed on each side. A wire or strong cord is fastened from one side to the other of the top frame about fifteen inches from the extreme rear point. This is used for hanging the hood upon the lamp, and makes it hang on an angle described in the illustration.