Microphotography is the art/technique of taking a photograph on a very small film or, more commonly, reducing a photograph to a print of very small size. Note that microphotography is very different from photomicrography, which is the art/technique of taking pictures of very small subjects through a compound microscope. There are different definitions of these two terms, and someone even considers them as synonyms. However, by and large, the definitions mentioned above seem to be the most commonly accepted.
Microphotography was especially popular in the UK in the Victorian and Edwardian periods. It was known in other countries, especially in Europe, albeit not to the same extent. At that time, it was very common for well-to-do people to have a microscope, and many Victorian ladies did spend a considerable amount of their free time inspecting microscope slides, cultivating tropical and unusual plants in greenhouses, attending popular-scientific lectures and pursuing other activities related to natural science. It was the time when ships brought back countless natural scientific marvels from colonies spread all over the world, scientists continuously announced major breakthroughs in chemistry, physics and biology, and society felt poised at the door of a golden era in which science was expected to solve all problems. Natural history museums were widely considered as an instrument for educating the masses and instilling in them high social virtues, and science was regarded as one the worthiest human enterprises.
Things started to change once Darwin's theory of evolution by natural selection became widely known. Science, although still regarded as indispensable to a modern society, was perceived as betraying the predominant social and religious values (especially the "Natural Theology" that combined religion, science and technology into a harmonious justification of the social status quo), and started an ambivalent love-hate attitude toward science among power-holders and society at large that continued and intensified, and still has profound social and historical effects. Nonetheless, microphotography, and the Victorian attitude to science in general, did leave a rich heritage. I do not known exactly how microphotography was invented, but the science craze had spawned a large aftermarket of scientific instruments, especially "recreational" microscopes and telescopes (a tradition that continues to-date in the form of toy microscopes and telescopes for children). Related items followed, including microscope slides, books and collection items. Victorian microscope slides prepared by the most famous makers (e.g., Suter, Wheeler, Watson) are still widely sought today, and typically of very good quality.
Photography was another of the favourite past-times of the period, with photographs taken of family groups instead of painted portraits, photographs commissioned at meetings and events, and pictures of exotic subjects streaming in from all corners of the world. Numerous recreational variants existed, like magic lanterns that projected pictures (sometimes hand-coloured) on walls, and viewers for stereo photography (of which Fisher-Price's View-Master was the direct descendant one century later, and still holds on in the PC era). Someone had the idea of combining microscopes with photography, and of creating entertaining pictures so small that a microscope was needed for viewing them.
Typically, microphotographs were mounted onto ordinary microscope slides and protected by a cover glass. Microphotographs range from the banal (everyday subjects, thrilling for the only reason that they had to be viewed through a microscope) to the inspirational (like the Ten Commandments), but are rarely interesting for the subject of the picture in itself. Naturally, they were made only in black-and-white (although micro-paintings in colour were also attempted).They are collectible items, and catalogs have been published of microphotographs prepared by the most famous makers. It seems that one of the early examples of microphotographs was a picture of Prince Albert built into a memorial ring made for Queen Victoria in 1861.
In the Cold War period, microphotographs and microfilms (the latter are similar, but physically larger) were often used to transfer secret information, and celebrated in numerous novels and movies. Large amounts of materials on microfilms are stored in libraries. Initially produced as a way to preserve or duplicate perishable documents and/or to save space, they have grown to become yet another liability, and will need scanning into a digital format for longer-term preservation.
Less than a century later, the technique of reducing pictures to microscopic sizes became an indispensable cornerstone of manufacturing solid-state electronics. Integrated circuits are produced by projecting the images of complex masks, reduced to much smaller sizes and stepped to repeat them multiple times onto photo-sensitive layers deposited onto semiconductor wafers, developing these layers, and subsequently etching or chemically treating the wafers on the areas left unprotected by selective removal of the exposed masks. Although this technique is rapidly approaching the limits imposed by light diffraction, it can be stretched by using ultraviolet light and in the future, possibly, X-rays or electrons, until radically new methods will become practical. The Ultra-Micro Nikkors and a few types of Zeiss S-Planar are among early examples of lenses designed for this purpose. Unlike normal types of camera lenses, these lenses for photo-mask exposure typically are optimized to work at a single specific wavelength and a single reduction factor.