Flash color temperature – Agenda for this month’s Measurebater’s Anonymous meeting

[Curtis N]

Objective – determine the range of color temperature of my Sigma Super flash unit at various power levels

Methodology – Shoot 18% gray cards with flash in a dark room at various manual power settings. Adjust aperture to compensate for flash power. Use the eyedropper tool of Raw Shooter Premium to determine color temp, averaging 4 readings on each shot.

Findings – General trend toward higher color temps at lower power settings (the opposite of what I expected).

This would seem to give some credence to the feature of Canon speedlites reporting color temp info to the camera, if indeed they vary as much as the Sigma.

I wonder if studio strobes vary this much too? Anyone ever tried to calculate it?

[jfrancho]

Hi, my name is John. I'm a measurebator. [group: "Hi John!"] Thanks, Curtis. Interesting stuff. I may have to run a quickie with my 430.

[FlashZebra]

I wonder if studio strobes vary this much too? Anyone ever tried to calculate it?
I used a flash colorimeter on the numerous Novatron and Speedotron studio flash heads at my camera club. I tested full power and in all the reduction modes on 12 flash heads (Full, 1/2 and 1/4 power) and at the reduced power modes on the 4 power packs (full & 1/2 power).

The color temperature did not vary much, at least nothing like the 800 degree Kelvin range you cite with your Sigma Super. I will try and ferret out the actual data and take another look, but I recall that no mater what I did to the heads, or power packs, (any settings) the color temperature stayed about the same.

The attached light modifiers, especially the several softboxes, really lowered the color temperature a lot more significantly than the power settings used.

Another member tagged onto the testing I was doing and did his own set of tests to his personal Alien Bee units. I did not see his actual data, but I recall that his overall conclusion was that the color temperature vairied some, but not a great deal. I will attemp to get a clearer picture from him on our next intersection.

Enjoy! Lon

[Titus213]

Hi, my name's Dave and I'm a measurebater... This is very interesting info. I shot a wedding last weekend using my 550EX and a rented 580EX. The color temperatures I noted between the two were confusing and frustrating. I am trying to schedule some testing with a couple of 580s and my 550 this coming week. If I can get results I will post them....

[jrsforums]

Here is a file, which I got from Doug kerr quite a while ago. While it is for the 550EX, I assume the 580EX would be similar....more than likely most Canon flashes would be spec'd tro fall in this range.

http://www.pbase.com/jrschwaller/image/65459002/large.jpg

[chtgrubbs]

Yes, studio strobes do vary with variable output, unless they have onboard electronics to compensate. It may not be much, maybe 100-200Degrees K, but it is enough to throw your color balance off when you need critical color matching for product photography or copying artwork. Then I use a color meter and adjust as necessary.

[Curtis N]

John, I'm confused by the three lines. Apparently they relate to different capacitor voltages but I didn't know this was adjustable?

[FlashZebra]

John, I'm confused by the three lines. Apparently they relate to different capacitor voltages but I didn't know this was adjustable?
It is unlikely the capacitor voltages are adjustable, but most likely you can fire the flash when a minimum charge is attained. But, if you are patient and wait, a much higher charge will be accomplished (with more light in the flash).

For an automatic flash that is often used in situations where the maximum burst from the flash is not necessary, jumping the gun a bit before maximum charge is achieved is often not a problem.

I suspect the flash will fire, even thought the capacitors are not at full peak charge. Most flash units will. This allows the marketing departments to tout fast recycle times.

So, my guess is that the three lines represent a minimum voltage, possibly just when the ready light just comes on, one intermediate setting, and finally a charge if you wait some significant amount of time after the ready light glows.

An alternated guess would be a minimum value that the flash would fire, even though the ready light was not fully on (or not a full glow), a value when the ready light actually glows, and finally a charge if you wait some significant amount of time after the ready light glows.

What is the nature of the “glow” function for the ready light on the EX 580? Does it have some sort of “intermediate glow” between “no glow” and “full glow”.

I do not have any Canon EX flash. Is there any possibility the ready light on the 580EX is actually red in color. If so, the color-coding on the graph may correspond to the graph colors, and would likely mean that the first guess above might be the "best guess" (at least for me).

Enjoy! Lon

[woffles]

I know the 580 has a quick fire function that will let it fire before the capacitor is fully charged. That may be the difference here.

[PacAce]

I know the 580 has a quick fire function that will let it fire before the capacitor is fully charged. That may be the difference here.
And that's when the Ready light glows Green. At full charge, it glows Red.

[FlashZebra]

And that's when the Ready light glows Green. At full charge, it glows Red.
But, there is a very good chance that even when the red light just starts to glow, the capacitors do not have "absolute" full charge.

To get that very last little bit in the capacitors, may take some time.

So, this likely explains the three lines on the graph.

The green line is simply the capacitor Voltage when the ready light starts to glow green, the red line is simply the capacitor Voltage when the ready light starts to glow red, and the black line is the capacitor Voltage after some relatively long time period and the capacitors are really at full charge.

Note the link below shows how a generic capacitor charges. This capacitor attains almost 2/3 of the ultimate value in only 1 time unit (called 1RC on the graph), and attains 89% of its full potential in 2 time units, but it takes 5 time units to get 99% of the full potential. For exposure purposes, it is very likely that 89% (or some other high value) is fine. The extra 11% would only contribute about 1/10 of a stop, so in practical use, it is just not worth waiting all that extra time for.

See: (look about half way down the page for the graph called "Graphs showing the current and Voltage for a capacitor charging)

http://www.kpsec.freeuk.com/capacit.htm

Enjoy! Lon

[jrsforums]

I know the 580 has a quick fire function that will let it fire before the capacitor is fully charged. That may be the difference here.

On the 580EX you can enable/disable "Quick Flash" with CF-8.

I think everyone else has explained the reasons for the 3 lines.

[René Damkot]

On the 580EX you can enable/disable "Quick Flash" with CF-8.
Only for continuous shooting. It's always enabled for 'single' shooting (the drive mode on the camera)

I think everyone else has explained the reasons for the 3 lines.[/QUOTE]

Then again, with quick flash, the GN is only 1/2 to 1/6 of full output, so I'ld expect the first two to three dots on the red and green line to be not there?

[DocFrankenstein]

This is much more significant than I thought. a 1000K

When I measured the bee's head the drop was around 400-500 K

[Double Negative]

The third line may also imply a CP-E3...