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The sensitivity and picture-signal output of iconoscopes have recently been increased by a factor of two or three times. The spectral response of the newer tubes more dosely resembles that of the eye and may be controlled by processing. "Dark spot" has been diminished by the use of a cylindrical envelope. The gun design has been changed to give a constant current as the beam is focused, and to prevent secondary electrons from the gun apertures getting into the primary beam. Use of the cylindrical envelope gives a better picture since a good optical window can be employed. Sandblasting of the mosaic improrves the picture contrast and quality by minimizing the specular reflection of the mosaic. More precise methods of measuring signal output, "dark spot," photoemission, and secondary emission of the mosaic, spectral response, and resolution are described.