Flash – text, week 13.

Flash has changed during the history of photography. The first recognisable use of flash was in 1839 when limelight (oxy-hydrogen, heating calcium carbonate in oxygen) was used to photograph microscopic subjects. A further variety of mechanisms were used, such as arc lamps, igniting magnesium with gunpowder and burning magnesium metal. The images were often poor, and the results literally explosive, and frequent dangerous. Flash really became available in 1887 when Adolf Miethe and Johannes Gaedecke mixed potassium chlorate with powdered magnesium to create ‘Blitzlicht’. However both the manufacture and use of the  ‘blitzlicht’ was dangerous. The process was refined and made safer, such that flash could function as fast as 10ms but it was still erratic. In 1929 a newer method was used using aluminium foil in an oxygen-filled container, with ignition being provided by a battery. This had the advantage of being less harmful to the subjects’ eyes and being more controllable. It also meant there was no smoke, an advantage in a studio, or noise, so the subject was less inclined to move. This method was further refined as they became smaller, more powerful and convenient. Soon cameras could be fitted with flash bulbs, Kodak coming up with the flashcube, which had four bulbs, enabling four flash photographs to be taken with each bulb, and was attached directly to the camera. For the professional a bulb was inserted into a concave dish that centred and condensed the light onto the subject. There was one drawback. These were one-use bulbs.
Fast forward and modern flash came into being. This was a compact integrated bulb, using an inert gas such as Xenon, powered by a battery pack or, in the case of the built-in flash, the camera’s own battery. The battery would produce a high energy arc that would create an intense flash of white light. The buit-in flash in the camera has a limitation, that is the fastest it will operate is 1/200s. To get around this, on the top of the camera a synchronising system was created and standardised called a hot shoe. This enabled an external flash to be synchronised with the camera, meaning illumination was provided at the same time as the shutter opened. It meant higher flash speeds could be created, depending on the power source, and a quicker refresh rate of the bulb. Modern flash now incorporate such things as infrared sensors to ensure the right amount of ‘light’ is released for the sensor, wireless flash, so that the photographer can trigger a flash that is remote to the camera, allowing angles of flash, or backlight, to be used, or multiple flash guns to operate.

There is one other aspect to be mentioned. The curtains in a camera. There are two. The first, which exposes the sensor and the second that covers the sensor. The speed these operate is determined by the shutter speed. However, although the two shutter system is standard it can cause problems with flash, with some photographs showing the shutter on the shot, with only half the photograph exposed.

Another is the image blurring. This is particularly noticeable at night with light trails.
If the flash is operated on the first curtain, the right is ahead of the subject, while on the second curtain it is behind, as shown below.

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