How the heck does a flash know what color temp it is firing off?

Seems like it would change with the flash age and environmental factors, yet the canon system (and other's I'm sure) communicate color temp to the camera.

Is it just a guess based on averages that were programmed into the flash??

Certainly there isn't a sensor in there??

Alien technology imparted only to the highest level flash engineers??

What gives?

Flash tubes are hermetically sealed with Xenon, a noble gas that is unaffected by age or environment. At the correct current density, a Xenon flash tube will emit full spectrum (white) light. Note that a speedlight fires the flash at the same power at all power settings, only the duration changes. There is no need for the flash to have a sensor, be programmed, or communicate color temperature to the camera. Speedlights are engineered to emit white light only, and will never vary (appreciably) in color temperature, even after millions of flash cycles. That is why you must gel your flash to change its color temperature. A flash tube can only be engineered to emit a specific spectrum and cannot be adjusted.

Good Morning!

This is what I was reading last night:

https://photography-on-the.net …/showthread.php​?t=1105424

the above seems to confirm that color temp varies with flash intensity, and varies just a bit even between shots at the same intensity.

then in this thread:

https://photography-on-the.net/forum/showthre​ad.php?t=836702

the following is posted:

Wilt wrote in post #9740135
And POTN's own 'measurebator' has stated similar reporting https://photography-on-the.net …php?p=3597162&p​ostcount=2 (he probably read what the manual stated!) If the flash color balance didn't vary (as yogestee is claiming it doesn't), there would seem to be no point in a flash communicating that information to the camera when the camera itself has Flash WB set, would it?!

A flash tube will catastrophically fail before it will be influenced by outside factors (age, environment, temperature, atmospheric pressure, altitude, relative humidity, phase of the moon etc.) Yes, color temperature can vary slightly at different power settings, but like I said, speedlights really only ever fire at full power - only their duration changes. The variation in color temperature is due to the differences in flash duration, not anything having to do with the flash's hardware. The information a speedlight is sending to the camera is basically just pre-programmed chart telling the Auto WB how much to compensate at various power settings. Not the flash nor the camera have any way to measure the color temperature.

the new 600EX-RT flashes have a little eye that looks at any gels added to the front of the flash, and can tell some cameras (i know it works with 1DX, but not sure of others) what colour Gel is on the flash, and adjust WB to suit (actually it fires a light through the gel, thru a pair of mirrors in the gel holder, and back into the flashgun)

typically though, flashes colour will change slightly with age, typically due to degradation of the plastics in the lenses, and slight colour change due to aging of the flash tube, colour also changes a little bit with flash power and duration, but these tiny shifts are unlikely to be noticed except for back to back comparisons

LostArk wrote in post #16505688
Flash tubes are hermetically sealed with Xenon, a noble gas that is unaffected by age or environment. At the correct current density, a Xenon flash tube will emit full spectrum (white) light. Note that a speedlight fires the flash at the same power at all power settings, only the duration changes. There is no need for the flash to have a sensor, be programmed, or communicate color temperature to the camera. Speedlights are engineered to emit white light only, and will never vary (appreciably) in color temperature, even after millions of flash cycles. That is why you must gel your flash to change its color temperature. A flash tube can only be engineered to emit a specific spectrum and cannot be adjusted.

A lot of people have this mistaken notion that the flash is always fired at the same power level each time but that is simply not true. It all depends on the amount of charge that's on the capacitor. Yes, at full charge, the power level the flash is fired at will always be the same but fire multiple consecutive flashes and the power level will decrease each time the flash is fired. To maintain a consistent flash output, then, the duration of the flash is increased as the power level decreases. The decrease in power level that the flash fires at will also change its color temperature. However, the color temperature at a certain power level is already know so it'll be easy for the flash to communicate this color temperature to the camera.

Echo63 wrote in post #16505965
the new 600EX-RT flashes have a little eye that looks at any gels added to the front of the flash, and can tell some cameras (i know it works with 1DX, but not sure of others) what colour Gel is on the flash, and adjust WB to suit (actually it fires a light through the gel, thru a pair of mirrors in the gel holder, and back into the flashgun)

so, alien technology, eh?

seriously though, wow. googled it and found this explanation of the 600 and it's gel detection feature, about half way down the page:

http://www.pointsinfoc​us.com …canon-speedlite-600ex-rt/

PacAce wrote in post #16505974
A lot of people have this mistaken notion that the flash is always fired at the same power level each time but that is simply not true. It all depends on the amount of charge that's on the capacitor. Yes, at full charge, the power level the flash is fired at will always be the same but fire multiple consecutive flashes and the power level will decrease each time the flash is fired. To maintain a consistent flash output, then, the duration of the flash is increased as the power level decreases. The decrease in power level that the flash fires at will also change its color temperature. However, the color temperature at a certain power level is already know so it'll be easy for the flash to communicate this color temperature to the camera.

so the flash is pre-programmed to know approximately what the temp is? (edit: pre-programmed at least as far as my 580 is concerned, and not considering the gel deal of the 600)

thanks for the explanation on the other stuff, didn't know the flash duration could increase with repeated firings.

The gel detection thing is a simple gimmick. All it does it automatically adjust AWB to Tungsten. The flash doesn't actually know what color the gel is. Nor is it possible for a flash tube to adjust its color temperature. The flash telling the camera what WB to use at what power level seems pointless and/or low tech enough that I wouldn't be surprised if they put it in the very first TTL flash.

I'm not sure why anyone would want to place a color filter in front of the flash and have the camera sense it's presence to adjust white balance. If one is placing the filter there to begin with it must be for some purposeful effect. So lets just say you are taking a portrait at sunset and wish to better balance flash color to ambient light, placing a warming filter on the flash will tell the camera body you are using this and then white balance adjusts to change the warming effect to the color white? Seems self defeating and useless.

RandyMN wrote in post #16506298
I'm not sure why anyone would want to place a color filter in front of the flash and have the camera sense it's presence to adjust white balance. If one is placing the filter there to begin with it must be for some purposeful effect. So lets just say you are taking a portrait at sunset and wish to better balance flash color to ambient light, placing a warming filter on the flash will tell the camera body you are using this and then white balance adjusts to change the warming effect to the color white? Seems self defeating and useless.

Or your shooting inside and trying to change the daylight coloured flash to match the tungsten coloured ambient (which you would have to change WB for, otherwise the pics would come out orange, now the camera does it itself)

LostArk wrote in post #16506264
The gel detection thing is a simple gimmick. All it does it automatically adjust AWB to Tungsten. The flash doesn't actually know what color the gel is. Nor is it possible for a flash tube to adjust its color temperature. The flash telling the camera what WB to use at what power level seems pointless and/or low tech enough that I wouldn't be surprised if they put it in the very first TTL flash.

It can tell the difference between a 1/4CTO and a full CTO though.
I actually don't know what effect it has on the WB with a 1/4 CTO, as the feature doesn't work on my 1D4 anyway.

I was born in the 1950's before color was invented. My entire universe is and has always been just black and white.

I have read about this thing called "color" it and it sounds just spiffy, even thought it seems a bit testy to deal with.

If I were born just a few years later, after color was invented, possibly I could help unravel the intrigue of this thread.

Enjoy! Lon

I was born even longer before color than Lon,
I let my new fangled camera set the color bit to AWB in the raw file and then use my fancy digital developer (so much less messy than the old liquid kind) adjust the color to my taste. Back in the darkroom ages, I had to have my lab guy do that with CC gels affixed to the enlarger when making the print. That was a real pain too.

hes gone wrote in post #16504699
=he's gone;16504699]Seems like it would change with the flash age and environmental factors, yet the canon system (and other's I'm sure) communicate color temp to the camera.

Is it just a guess based on averages that were programmed into the flash??

Certainly there isn't a sensor in there??

Alien technology imparted only to the highest level flash engineers??

What gives?

The flash doesn't know anything. The camera reads that E-TTL pre-flash and adjusts in microseconds.

FlashZebra wrote in post #16507015
I was born in the 1950's before color was invented. My entire universe is and has always been just black and white

I thought you were even older. I thought you were born when the world was Sepia.

cdifoto wrote in post #16507124
The flash doesn't know anything. The camera reads that E-TTL pre-flash and adjusts in microseconds.

But its color balance setting in the EXIF data is either a specific setting or AWB which it reads by assuming the sum of the color temps in the scene equal middle gray and makes an adjustment to get there. And is someone is saving JPGs in the camera it uses the info to process the JPG.

Incidentally, the gel reading feature in the 600EX only works with the three gels supplied with the flash. If one uses other gels, even stronger or weaker CTO. The flash indicates an error.