Stuff to Get Started With:
Technical warning: This post is really technical, but we tried to make it as readable as possible. And if you can believe it, this is actually the dumbed down version that does not address the issues of how capacitor switching or pre-flash ignition work.
We are regularly asked about broncolor’s ECTC color control technology. Photographers want to know does it work, how does it work, how to use it and when does it work. This post provides a quick overview. We can provide more advanced topics…just ask us!
Note Up Front: One thing we should point out up front is that ECTC is built into the broncolor Scoro packs. You don’t need to turn it on to make it work. In fact there is no way to turn it on of off. The only way to really modify ECTC is to activate the Scoro “speed mode.” Speed Mode shifts ECTC normal color balance to a slightly cooler flash, yet still consistent from flash to flash, color while enhancing recycling speed.
First let’s start with the basics, in order to understand color temperature control you need to understand how a flash actually ignites. We don’t want to get too technical, but basically, the flashtube is a hermetically sealed tube that is filled with an ignitable gas. The electrical connectors on the tube connect to the power source (which is normally a strobe power pack like a broncolor Grafit A4, Scoro A4s or Profoto 7a or 8a, etc). The gas has a really high threshold or resistance to ignition. So when the power pack triggers, current flows into the tube, starts to ionize the gas [ Ionize at Wikipedia], more current flows, heats up the gas, which lowers its resistance, which allows more current to flow, which converts the gas to a plasma state, and then BOOM! The full current load from the power pack comes rushing through the tube and a burst of light happens. But that burst of light, while really short, is actually made up of a constantly changing range of colors starting out really cool and then warming up at the end of the burst of light.
Lifecycle of a flash unit:
- Power pack charges the capacitors
- Flash is triggered and flash head ignition begins
- Capacitors unload their current to the flash tube
- Gas in flash tube get ionized by the initial current allowing current flow
- Heated ionized gas converts to plasma and allows the full load from the capacitors to come flowing in.
- Flash discharges and displays a burst of light.
- On advanced units: a “cut off” circuit will clip the gas explosion in order to control flash duration but clipping the flash curve also affects the color temperature because you lose the warm end of the curve.
Color Temperature Throughout the Duration of the Flash
To break it down a little further, when the flash ignites the light that comes out of it is not one color temperature. The color temperature changes throughout the fraction of a second of the flash. The color starts out really blue as the flash begins to discharge and then gets really red as the discharge tapers off. So an advanced flash unit that uses a cut-off circuit to control flash duration must actually pay careful attention to what part of the curve is being clipped or else the light coming out of the flash will be too blue.
On the other hand, with conventional flash units that don’t use a cut off circuit, a color temperature shift in the warmer colors can be noticed when the flash output is reduced. Part of broncolor’s secret is to manage the combination of the cut off with the balance of color throughout power range of the flash unit.
Broncolor ECTC Color Control
For over a decade broncolor has been using its own patented CTC (Color Temperature Control) process. It was revised and renamed as Enhanced Color Temperature Control (ECTC) for the latest Scoro power pack. ECTC coordinates flash voltage and flash duration. The result is consistent color temperature on every flash even at different power levels. ECTC even works in stroboscopic mode with up to 50 flashes per second; the temperature remains the same for each individual flash!
Flash Curves Without ECTC
The classical flash curve of all flash units has the following characteristics: At the beginning, “cold“ light appears in the ascending slope of the flash curve (comparable with the blue of a rainbow). With one of these simple flash units, when you lower the power to the head, the color temperature of the light becomes “warmer” (yellowish and reddish) because there is not as much blue from the initial burst at the steep part of the curve.
Note: It should be mentioned that this isn’t the only way to work without ECTC. Some high end products actually use a small preflash to try and balance out the curve. The trouble with the preflash is that it can cause ghosting or double images because the light output and flash duration will be dramatically altered creating a situation with two peaks in the curve rather than one spike.
Flash Curves with ECTC
ECTC adjusts the flash curve profile, so that the area under the flash curve or the selected amount of light, respectively, is produced with constant color temperature. Basically what you can see below is that the top line represents a head on a high power setting and the bottom line represents a head on a lower power setting. ECTC manages the output of both heads so that the total average output of light is equal in color temperature. On the top curve minimal cut off is implemented because the flash starts off with so much blue during the initial stages of the burst. On the lower powered head, less blue was introduced because of the lower power, and thus the cut off circuit can clip the red tail of the flash and provide a perfect 5500k.
Changing the Color temperature
On the Scoro, ECTC can also be used to deliberately adjust the color temperature of light in intervals of +/- 200 K. This means that you can actually go into the Scoro menu and set the color temperature that you want. You can use it to match changing ambient light or to compensate for aging yellowing softbox panels.
For more info visit broncolor.com