Sentence:  The microscope and <WSD>orthicon</WSD> are both selected to operate well into the ultraviolet spectrum , which means that all lenses must be quartz . 
Meaning of the word marked with <WSD> tags:  a now obsolete picture pickup tube in a television camera; electrons emitted from a photoemissive surface in proportion to the intensity of the incident light are focused onto the target causing secondary emission of electrons