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Flash Lamps for Cyber-Photography

The original motivation for the invention of the wearable computer was a desire for mediated reality, and for the ability to experience the world in a different light. It was that desire that gave rise to the Reality Mediator (RM).

A discussion of wearable computing would not be complete without a look at electronic flash systems, and their control by wearable computers. Early on, I created a wearable photographic lighting studio. This led to a genre of photographic imaging I called "dusting". Through a number of exhibits of this work in galleries in the early 1980s, this genre of cybernetic photography became more well known.

This page describes some modern flash systems, whereas there is another article describing early systems.

Modern commercial electronic flash systems

My favorite modern electronic flash system is the Lumedyne system, which has some of the nice features of early electronic flashes. The Lumedyne system is crude, simple, and reliable, and is also the world's most powerful wearable electronic flash that you can buy commercially, off-the-shelf, now. Unless you want to build your own wearable, the Lumedyne is probably the best choice. Many wedding photographers use the Lumedyne system, and you will also see these systems worn by professional photographers doing on-location work.

The basic unit contains eight 400 microfarad capacitors and a circuit to charge them to 480 volts. This unit is housed in a plastic case with a shoulder strap. A similar unit is made by Lumedyne's competitor, Norman Enterprises. The Norman unit is housed in a metal case, but is otherwise quite similar. I prefer the Lumedyne system for the following two reasons:

I feel better with the plastic (non conductive) case, because if anything went wrong with the system (so far I haven't had problems) I would not have metal touching my body. The Lumedyne system even uses plastic screws in the top. Although the metal housing of the Norman system might offer some shielding from radio interference, I have not had any problems with switching noise from my Lumedyne system getting into my computer or wearable camera or eyetap systems. It appears that despite the plastic case, the Lumedyne system does not radiate appreciably strong electromagnetic signals.
The Lumedyne system is cruder and simpler in its design, and is therefore easier to modify (and possibly more reliable as well).
The Lumedyne system is expandable, whereas the Norman system is not. For example, Lumedyne sells additional plastic boxes each containing an additional eight 400 microfarad capacitors, for an additional 8*1/2*400*480^2 = 8*50J = 400J of energy. These additional boxes snap together to build up the unit. I find that three additional boxes, which provide a total of 1600J (1600 watt seconds) can be worn comfortably, and allow a safety margin by staying well below the 2400J maximum rating of the flashtube.

Notes on safety

All the usual safety precautions of flashlamps apply. Don't stick your tongue into the lamp socket, etc... Respect high voltage, etc... One thing that might not be so immediately obvious is the danger of sharing batteries. I found the back kick from the flash circuit would sometimes have adverse effects on, or damage, other equipment, such as wearable camera systems. Therefore, I generally advise using a separate battery for the flash circuit, and one or more other batteries for the rest of the system (wearable computer, camera control units, hard drive, etc.). A diode bridge can help, but there is also the issue of safety, and it's nice to keep the flash isolated. I also trigger the flash through an opto isolator, or run it from fiber optics, so it is isolated from the EyeTap or from any computer system in close proximity to the body (e.g. electrodes on body for ECG, brainwaves, etc.).

Smaller flashlamps

The Lumedyne and Norman are both wearable. Some smaller units are hand-held rather than wearable, and are therefore more suited to hand held rigs than to wearable rigs. However, they may be modified for wearable use. My favorite handhelds are the:

Metz Mecablitz
Braun 900 or Braun 920

The Metz model numbers indicate the guide numbers in meters, e.g. the Metz 60CT-4 has a guide number of 60 in meters, whereas the 50MZ-5 has a guide number of 50. The following is a list of Metz guide number, its operating voltage, and the size of the capacitor.

45: 360v, 1700uF = 110J
50: 330v, 2700uF = 147J
60: 360v, 3300uF = 214J

(I calculated the energy from 1/2cv^2 and put it at right.)

Unlike the Lumedyne, the Metz has one big capacitor rather than several small ones. I use mostly the 50MZ-5. In stroboscopic mode, running at 30 hertz, the frame rate is suitable for an NTSC EyeTap or an NTSC wearable camera video capture, for electronic newsgathering (ENGwear).

Models 45 and 50 both have the capacitor in the handle, whereas model 60 uses a body worn capacitor, battery, and oscillator (shoulder strap).

There is something called a Metz Mecatwin, which is like the model 60 but it has a fatter handle, and the capacitor is in the handle. It is used in conjunction with another model 60, and becomes a slave system powered by the other model 60. These are no longer made, but if you can find one, they are great for modifying into wearable lighting systems.

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