Enlarger

An enlarger is a specialized transparency projector used to produce photographic prints from film or glass negatives, or from transparencies.

All enlargers consist of a light source, normally an incandescent light bulb shining though a condenser or translucent screen to provide even illumination, a holder for the negative or transparency, and a specialized lens for projection, though some, such as the Rapid Rectilinear or Aplanat^{[citation needed]} could be used in both camera and enlarger. Enlarger lenses, like the dialyte construction, are generally symmetrical in design or nearly so, optimised for sharp focus at 2x to 10x magnification. The light passes through a film holder, which holds the exposed and developed photographic negative or transparency.

Prints made with an enlarger are called enlargements. Typically, enlargers are used in a darkroom, an enclosed space from which extraneous light may be excluded; some commercial enlargers have an integral dark box so that they can be used in a light-filled room.

Josef Maria Eder, in his History of Photography attributes the invention of photographic enlargement to Humphry Davy who realised the idea of using a solar microscope to project images onto sensitised paper. In June 1802, Davy published in the first issue of the Journals of the Royal Institution of Great Britain his An Account of a Method of Copying Paintings upon Glass, and of Making Profiles, by the Agency of Light upon Nitrate of Silver. Invented by T. Wedgwood, Esq. With Observations by H. Davy in which he described their experiments with the photosensitivity of silver nitrate. Eder credits the first mention of enlargements after the announcement of the daguerreotype (unique images on metal plates) to John William Draper who in 1840, wrote prophetically in the American Repository of Arts; "Exposures are made with a very small camera on very small plates. These are subsequently enlarged to the required size in a larger camera on a rigid stand. This method will probably contribute very much to the practice of the art." In March 1843 Americans Wolcott and Johnson patented a means of copying and enlarging daguerreotypes.

In June 1843, Henry Fox Talbot in his patent for an enlarger for his calotype process which produced a paper negative, mentions that using lenses it is possible to produce a large negative from a smaller one, so having made such enlargements has a priority claim to be the inventor of a system for making an enlarged print from a negative, though it did not go into production and was not practical given the lengthy exposures required. In 1848, Talbot recommended to fellow photographer Thomas Malon the enlarging camera made by Thomas Ross of lens manufacturers Ross, Andrew & Thomas.

The advent of collodion negatives on glass in the 1850s made enlargement more practical. Achille Quinet's invention of 1852 used artificial light, but was inefficient, requiring very extended exposures. David Acheson Woodward's 1857 'solar enlarging camera' addressed that problem by tapping the brightest light-source then available – the Sun – with mirrors and a condenser.

Solar cameras, introduced in the late 1850s, and ancestors of the darkroom enlarger, were necessary because of the low light sensitivity of albumen and calotype materials used. A larger version of the 18th century solar microscope, they were first freestanding, a design analogous to picture-taking cameras but with the relative position of negative and lens reversed so that sunlight shone through the glass plate to be projected onto photo-sensitive paper inside the instrument. Mounted on a stand, they could be rotated to continuously face the sun.

Woodward's 1857 solar enlarging camera was a large instrument operated out-of-doors that could produce life size prints from quarter plate and half plate negatives with an exposure of about forty-five minutes, improved in the 1860s and 1870s with a clockwork heliostat to rotate the mirror in synchronisation with the sun's passage to concentrate its light on the condenser lens, while Désiré van Monckhoven's 1863 patent was for a modification of Woodward's design that had an appearance more like a modern horizontal enlarger.