When was zoom first invented for cameras?

For cameras, about 1902. Production of the patent from that year did not take place until about 1932 and was used in 35mm movie cameras as the first true zoom (meaning the focal plane did not shift appreciably when the lens was zoomed). The concept was first invented for telescopes around 1834, but it was a varifocal lens, in that it did not maintain focus when zoomed).