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due to the preponderance of light coming through its center, which is a simple lens. Prismatic No. 3 has been designed to break up the filament images more than does No. 2. The result of this is a great extension of the uniform range. It is evident that though the larger objective gives more light in all three cases, it does not, when used with the piano convex condenser, give appreciably more light in the uniform range.
SUMMARY
The results obtained so far may be summarized as follows :
1. The photoelectric cell can be made to give readings closely proportional to the total illumination, as measured by an optical photometer, delivered to an objective of any size, and for any differences of color normally met in practice.
2. There is no material gain in illumination for any of the condenser systems tried, by the use of a source larger than .7-inch on a side for a 2^-inch objective or .5-inch for a 1^-inch objective.
3. There is not more than 10 per cent, difference in the maximum total illumination given by any of the types of condensers when used with a source .4-inch or over.
4. For sources as large as .4-inch with any of the condensers tried, there is delivered to the 2^-inch objective at least twice as much light as to the 1^-inch.
5. Uniformity of illumination accompanies maximum illumination for all the condensers and objectives considered when used with uniform sources having an area as great as .3-inch square. On the other hand, for the 900-watt motion-picture lamp, although the prismatic condenser No. 3, when used with a 1^-inch objective gives a maximum illumination that is uniform, when used with a 21/^-inch objective, the greatest uniform illumination is 6 per cent, below the maximum. The piano convex condenser requires a decrease of 20 per cent, to obtain uniformity with the 1%-inch objective and over 50 per cent, with the 2^-inch objective, whereas uniform illumination can be obtained with prismatic No. 2 only by a sacrifice of 69 per cent, with 1^-inch objective though with a 2^-inch objective of but 20 per cent.
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