Mason & Coltman Image Intensifier

For fifty years, watching an X-ray image live meant sitting in a completely dark room. The fluoroscopic screen from the first blueprint in this batch is genuinely faint - so faint that radiologists wore red goggles for twenty minutes beforehand so their eyes would already be dark-adapted when they walked in. They were reading a barely-glowing screen with the rod cells of the eye, which have no colour vision and poor acuity, while standing next to an unshielded beam. **US 2,523,132**, "Photosensitive apparatus", Ruric C. Mason and John W. Coltman, assigned to Westinghouse, filed 10. August 1949 and granted 19. September 1950. It made the image thousands of times brighter, and it did it with two multiplied tricks. **Minification.** Take the light from a large input screen and land it on a small output screen. The same total light in a fraction of the area is brighter by the ratio of the areas - a 230 mm input onto a 25 mm output is roughly 85 times, from geometry alone, costing nothing. **Flux gain.** The input screen's light releases electrons from a photocathode; those electrons are accelerated through tens of kilovolts and slam into the output phosphor carrying far more energy than the photon that started them, making many light photons each. Another fifty times or so. Multiply them and the image is thousands of times brighter than the screen it replaced. The doctor could stand in a lit room, look through an eyepiece, and - crucially - point a television camera at it. **The patent's actual claim is about noise**, which is worth noticing. Its first claim specifies "an X-ray responsive fluorescent screen of the zinc sulphide type" AND "a photoelectric surface which responds substantially only to light in the blue, ultra-violet and higher frequencies". A photocathode sensitive to red light also emits electrons from sheer heat, which arrive as a snowstorm on the output. Matching the photocathode's threshold to the phosphor's blue emission keeps the signal and starves the noise. **You will build the minification half and measure it**, with a lens instead of electron optics - and then you will measure the thing the whole device cannot do, which is more interesting than the thing it can.