Flash light bulb
A flashlight bulb is a glass bulb filled with magnesium wire or magnesium foil and an oxygen-containing gas with lead-out power connections, which was mainly used in photography to generate a flash of light . Later the magnesium was replaced by zirconium . This ( pyro ) technology is largely out of date and has been replaced by (gas discharge in) flash tubes ( electronic flash ).
functionality
When a voltage is applied to the two electrodes, the wire begins to glow and ignites in the oxygen under a glaring light. The heat development and the resulting magnesium oxide usually cause the glass of the bulb to burst. Therefore, the later flash bulbs were covered with a plastic glaze. This layer becomes soft and prevents glass splinters from scattering into the environment. Flash bulbs used once cannot be reused.
Due to the chemical combustion process and the afterglow of the wire remnants and magnesia flakes, the duration of the light emission is up to 100 times longer than with an electronic flash, depending on the bulb . For this reason, the photographic "freezing" of very fast movements is only possible to a limited extent with flash bulbs.
The course of the light output of normal flashlight bulbs is relatively uneven, and the period between ignition and maximum light output is relatively long. This means that exposure times of 1/30 of a second or longer are required; with short shutter speeds, the camera shutter is synchronized in such a way that the ignition takes place before the shutter is opened (M synchronization). Because of the relatively long burning time, especially with cameras with a focal plane shutter, short shutter speeds are not possible; they would lead to very uneven exposure. In order to avoid this problem, so-called FP flash bulbs (from focal plane ) were developed, which had a comparatively long, even burning time and thus enabled the use of focal plane shutters.
Application area
Originally the flash bulbs were not colored. Clear flash bulbs have a color temperature of around 4,000 Kelvin and can therefore not be used with artificial light or daylight color slide film without a conversion filter. With the increasing popularity of color photography , daylight bulbs were increasingly produced in which the glass bulb or the plastic coating was colored bluish and the color temperature was raised to around 5,500 K. With an appropriate film, neutral color reproduction can also be achieved for indoor photos.
Flash bulbs were also installed together in a cascade. For the well-known Polaroid SX-70 camera , there were “Flash Bars” with ten bulbs each, which - attached to the camera - were ignited one after the other for each picture. Flash cubes contain four light bulbs. After each flash exposure, the cube was rotated 90 degrees manually, rarely automatically.
In the course of price reductions on the electronics market and further miniaturization, the electronic flash almost completely displaced the flash bulb. However, they are still used for niche applications due to a few advantages:
- Compared to portable electronic flash units, bulbs achieve a high amount of light with small dimensions and low weight.
- They are independent of the electrical power grid, in contrast to comparably powerful flash systems.
Large flash bulbs are still used for photography of caves, nocturnal architecture and landscape shots, illumination of large interiors (cathedrals, train stations) and in general in large format field photography with their often small aperture openings.
history
Glass lamps
The physicist Johannes Ostermeier , who worked at the Hauser company, discovered in 1928 that pure magnesium (or aluminum ), which was housed in a flashlight bulb in an oxygen atmosphere , could be ignited electrically and in a flash (in about 1/30 of a second ) burned with great brightness development. He had the technical invention protected by patents. These flash bulbs could only be used once and got very hot, but when they burst (occasionally) they only produced a small explosion . To prevent this, the flashlight bulbs were provided with a tough layer of lacquer, which was also colored light blue from 1950 to achieve a light color more similar to daylight. For a long time, uncolored flash bulbs for black and white photography were produced parallel to the blue flash bulbs required for color photographs. The light output was increased by using a reflector, which reduced the photographer's glare. The companies Osram , General Electric and Philips marketed this invention under the names Vacublitz, Sashalite and Photoflux until the 1980s, when the flash bulbs were increasingly miniaturized from the initially normal incandescent lamp design with Edison socket (screw thread). Typical “modern” flash bulbs had a guide number of around 36 (AG3) to 45 (AG1) at ISO100.
The first synchronously working flash on the camera was realized in 1935 with the Exakta model B from Ihagee in Dresden with "Vacublitz" bulbs from Osram . In 1949 Artur Fischer also invented flash synchronization. Agfa acquired the commercialization rights to the invention , which became a great success.
Lightning cube
N-flashcubes ( flashcube )
Sylvania introduced the flash cube in 1965, which contained four flash bulbs. It was a cubic hood made of transparent plastic, under which there were four lightning bulbs, each equipped with its own reflector. The connecting wires of these flash bulbs protruded from the bottom of the housing and were electrically connected to the camera. On the one hand, there were special flash units that recorded the cubes, and on the other, cameras with built-in mounts. After each exposure, the cube had to be rotated, which was done either manually or automatically. With better cameras, the flash cube mount was coupled with the film transport. After four flash shots the cube was used up. The ignition of an N flash cube required a battery and a capacitor, both of which had to be built into the flash unit and the camera. The guide number was 25 with a film speed of ISO 100/21 °, the light duration about 1/30 of a second.
X-lightning cube ( Magicube )
The battery required for the N flash cubes drove up the purchase price of the cameras and reduced their reliability. After all, the casual photographer could easily forget to change the battery in time. To get around these problems, Sylvania introduced the Magicube, a new lightning cube with mechanical ignition in 1970 . This was marked with an X on the top of the housing and was not compatible with the N flash cubes. X flash cubes could only be used with cameras that had a corresponding socket. The manufacturers often identified these models with an X in the model name, for example Kodak Instamatic 233-X . When the camera was released, a plunger came out and pressed into a designated opening in the flash cube. In doing so, he released a taut wire that snapped against a pin that was in turn worked into the glass bulb and ignited the shock-sensitive pyrotechnic filling there. (The sometimes widespread explanation that a piezo element would trigger an electrical impulse and thus the flash is wrong.) Most cameras for pocket and Instamatic film were equipped with X connections . X-lightning cubes were slightly larger in size than N-cubes. Their guide number was also 25 at ISO 100/21 °.
Topflash
When using flash cubes on pocket cameras , it was easy to get red eyes when taking photos of people . The reason for this was the small distance between the lens and the flash bulb. This was remedied by a spacer (Magicube Extender), which was often supplied with the cameras. Since its use could easily be forgotten, Philips presented a solution protected against incorrect operation with the Topflash. It was a tall but flat case with eight lightning bulbs, which were laid in two rows on top of each other. The housing had roughly the same area as a conventional pocket camera, so that when it was laid flat on the camera it usually fit easily into the camera bag. A Topflash had two connections, one on the top and one on the bottom. First one of the two connections was plugged into the camera, then the top four bulbs could be ignited one after the other. Turning the top flash allowed the remaining four bulbs to be used. This ensured that there was always a sufficient distance between the lens and the light source. A top flash had electrical contacts and was ignited with a piezo element in the camera, so it did not need a battery. From behind you could see the still intact lightning bulbs by a yellow point that disappeared when it burned down. Corresponding to the flash cubes, the guide number was 25 at ISO 100/21 °. The Topflash became very well known with the extremely successful Agfamatic Pocket 2008/3008/4008 series . The "8" in the names indicated the eight lightning bulbs. But there were also companies that had installed 2 × 5 light bulbs.
Flashbar
For Polaroid instant cameras , there were special single-use flashes with ten flash bulbs, which were placed next to each other in a housing with five on each side. As with the N-flash cubes, they were fired electrically - since the cameras in question worked with a battery anyway, this was not a disadvantage; the camera electronics automatically controlled the next ignitable lamp. The guide number was a high 45 at ISO 100/21 ° with regard to the low-light lenses of the instant cameras (due to the large focal length).
See also
Individual evidence
- ↑ The element magnesium
- ↑ The element zirconium
- ↑ The brightest lightning in East and West; Special exhibition about Eugen Nosko in the Technical Collections Dresden 2010
- ↑ US patent number 1,776,637 of September 23, 1930 for Johannes Ostermeier , accessed on September 19, 2010