Harold Horace Hopkins FRS (6 December 1918 – 22 October 1994) was a British physicist. His Wave Theory of Aberrations, (published by Oxford University Press 1950), is central to all modern optical design and provides the mathematical analysis which enables the use of computers to create the highest quality lenses. In addition to his theoretical work, his many inventions are in daily use throughout the world. These include zoom lenses, coherent fibre-optics and more recently the rod-lens endoscopes which 'opened the door' to modern key-hole surgery. He was the recipient of many of the world's most prestigious awards and was twice nominated for a Nobel Prize. His citation on receiving the Rumford Medal from the Royal Society in 1984 stated: "In recognition of his many contributions to the theory and design of optical instruments, especially of a wide variety of important new medical instruments which have made a major contribution to clinical diagnosis and surgery."

Hopkins was born into a poor family in the slums of Leicester in 1918 and his remarkable mind was recognised early on. Due to his own genius and the good fortune of having the support of both his family and teachers, he obtained one of only two scholarships, in the whole of Leicestershire, enabling him to attend The Gateway Grammar School. There he excelled, especially in the arts, English, History and other languages. However, the Headmaster, recognising his exceptional gift for mathematics, directed him into science.

So he read physics and maths at University College, Leicester, graduated in 1939 with a first and then ^{[citation needed]} began a PhD in nuclear physics in the Department of Physics (now the School of Physics and Astronomy). However this was cancelled on the outbreak of war, and he went to work for Taylor, Taylor & Hobson where he was introduced to optical design.

Hopkins was inexplicably not given reserved-occupation status, which led to his being called up and being briefly trained in blowing up bridges. (He was a natural, quickly rising to the rank of 'acting unpaid lance corporal' and winning a prize for his speed at dismantling and reassembling his rifle.) The error of this placement soon became apparent and he was set to work on designing optical systems for the rest of the war, at the same time working on a thesis for his PhD, which was obtained in 1945.

He began a research fellowship at Imperial College London in 1947, lecturing in optics. The next twenty years saw him emerge as one of the foremost authorities in the field of optics. In addition to his own work, he attracted a large number of high quality PhD students from all over the world, many of whom became senior academics and researchers themselves. His reputation as a teacher was second to none. When he moved to Reading University in 1967 to take up the newly created chair in optics, many of his former MSc students at Imperial would travel to Reading to attend his lectures. He always believed that his primary responsibility was his teaching and that the research came second. However he was also totally convinced that teaching and scientific research were vitally important to each other. "Only when you try to teach something do you discover whether you truly understand it."

He used mathematics in the subject. The development of the mathematical description of the behaviour of optical systems was at the centre of his life's work in physics – the application of which produced many world-famous inventions. He chose to remain at Reading in the post of Professor of Applied Physical Optics until his retirement in 1984, declining the numerous top appointments he was offered. He believed the continuation of his teaching and research work to be more important and far more rewarding personally. However, he took great delight in having conferred on him the Honorary Fellowships of all the medical Royal Colleges in Britain, together with the highest awards of many of the world's premier scientific bodies including (in 1973) the Fellowship of the Royal Society itself. He was awarded the 1990 Lister Medal for his contributions to surgical science. The accompanying Lister Oration, given at the Royal College of Surgeons of England, was delivered on 11 April 1991, and was titled 'The development of the modern endoscopes – present and future prospects'. This award, for his work on endoscopes, was unusual in that normally it is given to someone in the field of medicine. He was awarded the 1978 Frederic Ives Medal by the OSA, where he was also a society Fellow. What is less well-known about Harold Hopkins is that he was also a politically committed man of the left, being an early member of the Communist Party of Great Britain. Coming from a poor and under-privileged background, he understood how essential equal opportunities and good education were if ordinary working class youngsters like himself were to prosper in society.

Following a request in the late 1940s from the BBC, who wanted a single lens to replace the classic "turret' of different focal length lenses, he produced the familiar zoom lens. Although there had been earlier attempts to produce a lens which could achieve continuously varying magnification without re-focusing, none of them could provide a good quality image throughout their zooming and aperture ranges. The design of a zoom lens is enormously more complicated and difficult than that of a fixed focal length. The performance of the Hopkins designed zoom lens revolutionised television images, especially outdoors-broadcasts and opened the way to the ubiquitous use of zooming in modern visual media. It was even more remarkable for being produced pre-computer, the ray-tracing calculations being performed on large desk top electro-mechanical machines such as the Marchant Calculator. Even so, the early zoom lenses still fell short of the fixed lenses. The application of computer design-programs based on his Wave Theory of Aberrations in conjunction with new types of glass, coatings and manufacturing techniques has transformed the performance of all types of lenses. Whilst zoom lenses can never out-perform fixed focal lengths, the differences are no longer significant in most applications.

The ancient Romans knew how to heat and draw-out glass into fibres of such small diameter that they became flexible. They also observed that light falling on one end was transmitted to the other. (due to successive reflections from the internal surface of the fibre.) These multiple reflections mix the light beams together thereby preventing an image from being transmitted by a single fibre – (more accurately, the different path-lengths experienced by individual light-rays alter their relative phases rendering the beam incoherent and thus unable to reconstitute the image.) The end result is that the light emerging from a single fibre will be an average of the intensity and colour of the light falling on the incident end.