Hey Buddy, You Need A Light?
How did we get here?
The journey has affected how we have ended up with these marvelous, portable electronic flash units. (Learn more at Wikipedia.)
Someone figured out that magnesium powder in a handheld trough could be lit during the exposure creating a bright light. The exposure times were reduced…maybe no more need for the head gear?
Flash powder was explosive. It had to be handled carefully. (Talk about a safety problem!)
Flash bulbs were magnesium strands in a glass enclosure. They were placed in a reflector and, when the camera shutter was released, a circuit connected to the shutter mechanism closed a switch which caused an electric charge (from a battery) to ignite the magnesium. It burned brightly. Once.
The photographer could eject the bulb, replace it with a fresh one, wind the film, and shoot another shot. In well practiced hands, this could be done quickly and efficiently.
Bulb were quite powerful and, compared to small electronic flash units, likely better and filling a room with light. (They needed to be so because films weren’t as sensitive as what we have available, today.)
Engineers and scientists came up with a circuit which combines batteries, charge pump circuits, large capacitors, and discharge tubes. The result was electronic flash. Some considered this an improvement over flash bulbs. For sure, you didn’t need to worry about disposing of all that burnt magnesium and glass and metal.
The discharge in early flash units was fixed. You got a full blast and any adjustment to how you’d light a scene had to be done with changes in distance and F-stop. With practice, it was easy.
If your flash battery could produce 50 shots then you got 50 shots.
Someone developed a circuit that used an electric eye sensor in the flash head. This gave the photographer control of F-stops, making adjustments to fit the need. The electric eye circuit, with the F-stop parameters dialed into its control, could control the amount of high-voltage (which is what the charge pump and capacitors are all about) being discharged across the flash tube. The eye measures the flash output, and when enough light is produced, the circuit closes and the remaining charge in the system is discarded.
So, the good news is the flash produces just the right amount of light for the photo, but you still only get 50 shots.
Along come Thyristors. These circuits allow the flash system to use the electric eye, but the excess power is not wasted.
Same results, but now you get more than 50 shots. Yay!
You have to set off a flash using some kind of trigger. It could be a wire from the camera to the flash head. It could be a wire inside the camera, itself, if the flash is built into the camera.
With multiple flashes, though, you need a wireless way of setting off the flashes. There are a couple options: optical and radio.
Optical means that the flash head has a sensor that looks for a flash-like discharge. If it detects one, it sets off it’s own flash. This is great if you are the only photographer and have your own equipment. But, if you are in a crowded room with other photographers, then their flash discharges will start setting off your own flash heads. That’s not good.
Radio solves this problem to some extent. A receiver circuit listens for a signal from a transmitter. If the signal is just the right kind, then the flash is set off. The problem still exists if you are in a room with multiple photographers using the same systems. The good news is that modern (expensive) radio control systems use channels to separate their equipment from everyone else’s. Of course, if another photographer is using the same channel…
Newer flash systems used optical flash controls but with a twist. The computers inside the flash heads put out small pre-bursts of flash, encoded in a way that is unique to their system. These pre-bursts can do a lot of interesting things in terms of controlling other flash heads, or banks of flash heads.
Cameras got smart over time. With computers built into them, and sensors that could measure the light coming into the camera, and analysis techniques for sorting out all the stuff that goes into making a beautiful photograph, it made sense to expand this kind of control into the flash system. So, TTL (through the lens) was born.
A flash mounted on a camera, or connected through a specialized cable, can have it’s flash discharge controlled by the “system”. This can be extended to other flash units that are controlled by that wireless optical pre-burst magical system discussed above.
It just costs money and time (for practice) to get it right…and don’t forget to read the instruction manuals!
What’s useful about electronic flash is that it’s portable. LED technology is coming into vogue and it has some good points. For one, working with a constant light source is nice because you can see the effect of the light (specularity, direction, intensity, reflection) on the subject as you are working. This is true if it’s just one light or several.
There’s no flash sync (wires or wireless) to worry about.
LED’s may not be as powerful (yet) as a flash, but can be purchased for about the same amount. Something to think about.
Here’s a piece on Luminous Landscape that looks at what’s new in LED’s.