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1949
CATHODE-RAY OSCILLOGRAPHY
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rather widely separated portions of the spectrum, phosphorescence being amber in color, and the fluorescence a blue having the same characteristics as the Pll screen. Another problem is that of the resolution required in the final recording. Certain screen types are considerably better in resolution than others. For example, the Type P7, being a two-layer screen, tends to diffuse the image more than the Type PI which is a thin homogeneous material. The requirement of high resolution also places certain limitations on the film type. As a general rule, the higher speed films give relatively coarse-grained images. If extremely high speed is desired, it is also necessary to use developers whose activity is such that they also
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Intensity
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Magnification, M (object -image ratio) Fig. 22 — Relation between magnification and image intensity.
tend to produce relatively coarse images. The coarseness of the grain of the images may be so great as to spoil completely the resolution of an otherwise good recording. Where sufficient exposure is available, it is better to use .a relatively slow-speed film such as Panatomic-X which, even under adverse development conditions gives fine-grained images which can be enlarged considerably for study. If speed is the prime requisite, then the fast coarse-grain films and fast coarse-grain resulting developers must be used. The use of faster sweeps will then enable the apparent resolution to increase.
There are two types of special high-speed films manufactured by the Eastman Kodak Company specifically for oscillography. These are known as Linagraph Panchromatic film and Linagraph Ortho