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1886, of echoic origin. Gained popularity c.1917 as aviators began to use it; zoom lens is 1936.
To show a smaller area of an image at a higher magnification ("zoom in") or a larger area at a lower magnification ("zoom out"), as though using a zoom lense on a camera.
Unlike in an optical system, zooming in on a computer image does not necessarily increase the amount of detail displayed since this is limited by what is actually stored in the image. Similarly, you cannot zoom out beyond the full size of the image.