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as well as for incandescent lighting. Therefore two arc spot lamps were designed where the light crater of the arc was taken directly into the Fresnel lens
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Figure 6
with a great improvement in the beam
pattern over the 24-36in. Sun Arcs formerly used. Fig. 7 shows the new equipment.
Fig. 8 shows the beam pattern of a 36in. Sun Are with the always objectionable dark centre caused by the shadow of the arc mechanism, and Fig. 9 shows the beam pattern using the Fresnel lens.
Importance of Constant Are Current and Crater
In addition to this very advantageous beam pattern here again it was possible to design equipment which was much smaller in size than the old type of are lighting equipment and which had many new uses which were formerly impossible. This arc equipment had to be used nearer the microphone in colour photography, therefore a new degree of quietness had to be built into its mechanism. Since fluctuations in the quality of light were not permissible, it was necessary to ensure constant colour quality by designing a fixed resistance so that the amperage at the arc
would always be kept constant, and an automatic feed so that a stable crater could be held. Here again a light weight yet rugged equipment has been evolved with several new features which make for greater ease of handling on the set. All the control mechanism is mounted on the. back plate of the lamp, so that for switching, striking and locking of this equipment the operator does not have to reach around the side of the lamp, and for trimming two large doors are mounted on the side of the lamp to facilitate the trimming.
The Correct Use of Diffusers
It is often found necessary to use either diffusers or filters in photographic light
Figure 7
ing. The Fresnel lens spot lamp is extremely well designed in this respect since diffusers are much smaller in diameter, and, therefore, more easily handled and more easily maintained. Sturdy diffuser clips are permanently mounted on the lamps. The subject of diffusion is one that warrants considerable thought in most studios.. A rather diligent study of