They usually contain a modeling light, an incandescent light bulb close to the flash tube; the continuous illumination of the modeling light lets the photographer visualize the effect of the flash.
22.
This method means no charging times are required, and flash rates can be much faster, but drastically reduce the lifetime of the flash tube if powered for excess amounts of time.
23.
High-end flash units address this problem by offering a mode, typically called High Speed Sync ), which fires the flash tube multiple times during the time the slit traverses the sensor.
24.
If this current limiting was eliminated, the flash tube would attempt to draw high currents from the electricity source, potentially tripping electrical breakers or causing voltage drops in the power supply line.
25.
Some strobes even offer continuous mode, where the arc is sustained, providing an extremely high intensity light, but usually only for small amounts of time to prevent overheating of the flash tube and thus breakage.
26.
More-subtle filters are needed to correct for the difference between, say 3200 K and 3400 K tungsten lamps or to correct for the slightly blue cast of some flash tubes, which may be 6000 K.
27.
The flash tube is a cold-cathode device filled with xenon gas, used to produce an intense short pulse of light for photography or to act as a stroboscope to examine the motion of moving parts.
28.
The 1955 Flash-Matic remote system, invented by Eugene Polley, used a highly directional photo flash tube in the hand held unit that was aimed at sensitive photoreceivers in the four front corners of the television cabinet.
29.
The Speedlite 550 EX, 580EX, 580EX II and the 600 EX-RT ( when used as an optical master ) flashes use modulation of the pre flash from the main flash tube for communicating with slave flashes.
30.
If the capacitors were charged to a voltage high enough to ionize the tube, the result would be no longer a flash, but a continuous arc as the voltage is sufficient to maintain ionization in the flash tube.
