2012-09-30

Flash bulbs

50 years ago the electronic flash has already been invented, but it only prevailed among amateur photographers slowly in the course of the 1970ies. In particular it displaced the flash lamps using flash bulbs. In my collection I have actually three such external flash lamps, one is the Zeiss Ikon Ikoblitz 5, the others are similar. In addition I own two cameras with (more or less) build-in flashes, Kodak's Brownie Starflex and Polaroid's J33. Together with the latter I got a pack of unused Sylvania flash bulbs. I thought, this is the perfect opportunity to add a second post about flash bulbs. The first one was in German, so this here has to be in English.



Flash bulbs are based on an idea by Paul E. Liesegang. In 1861 he proposed to use Magnesium as a light source for photography as it burns off very brightly. Other people developed early open flash lamps using Magnesium powder. In 1899 Josua Cohen was granted US patent No.  636,492, a pretty dangerous apparatus, which would only be handled by professional photographers. It was a kind of logical next step to move the flash "explosion" into a glass bulb. Johannes Ostermeier received US patent no. 1,776,637 for this in 1930. First flash bulbs were big and looked like aluminum foil filled light bulbs using the same screw mounts we still use for normal lighting. Over the years the flash bulbs got smaller and eventually use fine magnesium wire (alternatively, zirconium and aluminum-magnesium alloys) in an oxygen-enriched atmosphere. The circuit of a flash bulb lamp is quite simple, the switch is the shutter release button of the respective camera, connected via a standard sync cable or later the center contact in the accessory shoe (called the "hot shoe"). Once ignited, flash bulbs can't be used again. A plastic coating prevents splintering. Some coatings are blue to create the right light color for color daylight film. This Sylvania bulbs here were clear, as the Polaroid would normally only shoot B&W images.


On the pack there is this BLUE DOT statement, which is a quality attribute. The little blue indicator dot (behind the two electrode wires) ensures the user that this bulb will most probably fire. It consists of anhydrous cobalt (II) chloride. If the bulb is broken and moisture gets into it the dot's color change from blue to light pink. As you can see on the aperture table on the back of the flash bulb pack, these guys make decent light. Today's electronic flashes only achieve guide numbers of 180 (at ISO 100) in case of larger external models, built-in flash tubes in cameras often reach only 30-60. My first flash, the Vivitar 3200 had a guide number of 64 (distance range in feet = guide number divided by aperture).
Many lighting companies produced flash bulbs. Osram used to be market leader in Germany, Sylvania was big in the US. Today, both companies belong together but don't produce flash bulbs anymore.
It should be mentioned, that flash bulbs have a different time/light characteristic than electronic flash tubes, which illuminate the scene in fractions of a second, sometimes even 1/10,000 sec or faster. Flash bulbs are kind of slow burning and allow the use of focal-plane shutters at almost every (fast) speed. They produce continuous light for the time taken for the exposing slit to cross the film gate. For this they have to be fired before the first shutter curtain begins to move, which is called M-sync; the X-sync used for electronic flash fires only when the first shutter curtain reaches the end of its travel. Many cameras from the 50ies and 60ies have a switch to choose between both options. More information about the history of flash lights in photography can be found here or here (in German).

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