usingaflashbulb 3faction edit
| Field | Photography |
| Went Obsolete | Late 1960s |
| Made Obsolete By | Inexpensive electronic strobes |
| Knowledge Assumed | Determining the correct lens aperture by dividing the bulb's guide by the camera to subject distance |
| When useful | Flash bulbs are much brighter than all but the most expensive strobe units. Flash bulbs are useful when you need a lot of light to properly illuminate a photograph |
Flash bulbs are small, sealed glass containers filled with magnesium wires in oxygen. An electrical contact at the bottom allows the bulb to fire from a battery charge when the camera shutter is opened. They can only be used once. Immediately after use, the bulb is very hot and can cause burns.
To use a flash bulb, one needs to know the bulb's Guide Number and the ASA/ISO film speed (or sensitivity setting for a digital camera). This information was listed by the manufacturer on the package. The equation to determine the proper lens opening is: Lens Opening = (guide number / distance) * (Film Speed / 100) A common guide number was 200 at ASA 100. If you were using the dear departed ASA 25 Kodachrome film and your subject was nine feet from the camera the equation which you would do in your head would be (200/9)*(25/100)=5.6. You would then set the lens aperture to 5.6 and take your picture.
Another skill required for flash bulb use is insuring a good electrical contact at the bulb's base. This is accomplished by rubbing the bulb's base on one's trouser leg and/or licking the base prior to inserting the bulb into the flash holder.
An interesting bit of movie lore is that the light sabre handles in the original Star Wars movie are in reality flash bulb holders (with the reflector removed) manufactured by the Graphlex company in the 1940's.
