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An enlarger is a device used to produce photographic prints from photographic negatives. It makes a projection of a negative's image plane to a larger image plane on the surface of light-sensitive photo paper. The exposure is controlled by a shutter or by a timer for the enlarger's electric light source (or simply by the user with the on/off switch), and through the enlarger lens' aperture setting. Ancient enlarging devices like the Simplex used daylight, others used gas light as light source--nowadays a very high-wattage electric bulb is typical.

At its core, there is little difference in operation between an enlarger and a projector: a light source is held some distance behind a transparency (usually negative film, in this case,) which sits at the focal plane of a lens. Assuming the transparency is perfectly flat on the focal plane (accomplished by moving the lens nearer to or farther from the transparency), a sharp image is thereby projected in a light cone. In a projector, this light cone would strike a screen and be observed directly. In a typical enlarger, this light cone is instead directed down at an easel in which a piece of photo paper has been placed, in order to expose a positive image on it. The loading and developing of the paper must be done under a safelight or in darkness. Typically the process is to activate the enlarger's light with the negative loaded, but no paper present, in order to focus the lens and adjust the height of the enlarger head (size of the image) and the position of the easel, deactivate the enlarger, and then load the paper into the easel and reactivate it for the required time--for many paper processes, this is a long, long exposure compared to film, often measured in increments of ten seconds.

Major manufactures that have produced enlargers include.

Enlarger lenses

Enlarger lenses should have almost no curvature of field. Since film-based analog photo hobby declined in digital photography age many used enlarger lenses are available, and usable as experimental camera lens when a way is found to adapt them to a Micro Four Thirds camera or a similar system camera. Many recent enlarger lenses have a 39 mm mounting thread.

Enlarger lens makers have included:

Enlarger timers

Enlarger timers are electromechanical or electronic devices that maintain printing exposures accurately timed. Enlargers plug into the timer which turns the light on and off for a determined time.

Timers have been made or sold by: