Paul C. Buff, Inc. Technical Forum

Feel free to comment or ask questions about this.

A great piece of info to dismistifi the light things :D :D :D
I have for some time geting the most info for other brands to came also to numbers you put here.
A fantastic way of marketing ;) ;) ;)

Hi. I don't quite understand this chart.

It appears that you're showing here that the AB800 always puts out a flash with a color temperature some 375 degrees below what it should be. So I read that to say that if I am expecting it to output at 5600-degrees Kelvin, it's actually going to be 5225-degrees Kelvin. And I interpret the chart to say that it uniformly creates a lower color temperature from the highest power to the lowest power, but that it is at least consistent (and therefore, consistently correctable in post, yes?). Is there some chance that the chart is meant to say "plus or minus 375-degrees," rather than just, "minus 375-degrees?"

It also appears that at full power, the AB800 has a shorter t.1 flash duration than any of the other flashes shown in the chart, though I indeed see the advantages of the much shorter t.1 duration in "action" mode if I were needing to shoot that way.

So it seems that for me, shooting portraits in a studio or even people dancing at a wedding, I would gain from having an Einstein in color accuracy mode because it's only going to vary by 50 or so degrees Kelvin from shot to shot and as I lower and raise power. But if the color output of the AB800 is consistently lower than normal from shot to shot and power to power level, I'm getting the same result from the sake of having a series of photos with a pretty constant color temperature. If I'm trying to stop a baseball without ghosting, which I never do, I need the Einstein, but otherwise I should be find with the AB800 or even one of the lower wattage AB's with an even faster t.1 time. Am I misinterpreting all this?

The spec of -375K is the color shift from full power (5600K) to minimum power (5225K). All voltage controlled lights are going to shift by 75-90K per stop as you dial down and lower the voltage. Once an output is set, the shot to shot color will be consistent, provided enough time is allowed for the light to recycle. Other manufacturers claim +/-50K, which is plausible for shot to shot, but not power level to power level, and they do not specify which, and many people assume it is from power level to power level and shot to shot.

Yes, the AB800 does have a faster flash duration at full power, as it is a lower powered light. But it is important to note, the E640 can achieve twice as fast flash duration at the same power level in action mode, or similar flash duration in color mode.

Thanks for getting back to me, TS. I guess I was confused by why you would list the -375K number twice, and was reading that as it putting out 5275K at full power. So, why do you list the number twice? And on that same note, should I read the chart to say that the Einstein is kicking out something like 6400K when it fires? You list it as being +800 or more from high to low, and there you're using two different numbers. I generally consider myself pretty good at reading a chart, and am somewhat wise in a technical sense, but the information you've presented raises more questions than it resolves (for me.)

On a somewhat related issue, why does the flash duration increase when the power level is decreased? This appears not to be the case with my Nikon flashes, which go from something like 1/600th of a second at full power to 1/13000th of a second at 1/64th power. Is it just because a speedlight will have such a smaller tube, or is there some other limiter being placed on the capacitor so that it's able to cut off quicker (on the Nikon)? The longer flash duration doesn't quite make sense to me on Alien Bees. I thought perhaps it's because you've got a larger flash tube, but at full power it's got a lot more to cool off after firing, so I'm not able to figure out what the reason is for the t.1 and t.5 durations.

By the way, I've been a Bee owner for years, and really enjoy them. Thanks for putting together such a solid product, and for being so upfront with your customers about what they're actually buying.

The top numbers in a cell in the chart are the specified values. The bottom numbers are the values Paul actually measured.

Yes, the E640 will have a color temp of 6450K-6500K when set to minimum power and action mode. Color mode, it will still be 5600K +/- 50K at any power setting. Again, this is the specified color temperature vs. actual measured temperature (it is within 50K).

Flash duration can be controlled in one of three ways: 1-The amount of available storage of energy ( more/fewer capacitors, larger/smaller capacitors, etc). 2-The amount of charge in a capacitor (is a given capacitor fully charged, or partially charged). 3-Interupting the flash pulse (IGBT).

The reason a B800 has a faster flash duration than an E640, or other lights on the list (at full power) is because it has less power to emit due to fewer capacitors. Assuming all capacitors are the same size, and since they are all at full, they are operating on the same voltage, less stored energy equals a faster discharge. But, when the power of an AB is reduced, the capacitor is not fully charged, and is charged at a lower voltage. Lower voltage yeilds a longer discharge. ALL studio lights that have a dial or slider will exhibit this same result. Flash durations roughly double between full and 1/32 power. Almost all of our lights use this type of power control, except Einstein and the 5000 and 10000's.

The number of capacitors is fairly simple. Just like unloading one truck or two trucks, the more trucks or capacitors you have, the longer it takes to discharge them. These are typically adjusted by mechanical rocker or toggle switches. Our original 5000 and 10000 lights used capacitor banks exlusively. Zeus and X-series use a combo of capacitor switching and voltage sliders.

Einstein and Speedlites use IGBT's to cut the tail from the flash duration. All flash outputs peak rapidly, and trail off in intensity. IGBT's act kind of like a valve and keep the residual power in the "tail" from being emitted. The less tail you have, the less light you get on your subject. The less tail you have, the less time it takes for the entire flash duration. IGBT's have been historically more practical in speedlite type applications, which is why most lights increase in flash duration with a decrease in flash power.

Outstanding explanation. Thanks very much for taking the time to do that.

Sorry I haven't been in on this discussion . . . I'm on vacation.

Lest anybody be dismayed that Einstein has a significant rise in color temperature in Action Mode at low power and fast durations, this is the physics of the IGBT method of achieving fast durations. You will see the same effect on extremely expensive Broncolor IGBT packs and on speedlights when used in manual mode at reduced power.

A good partial explanation of why can be found at http://blog.bronimaging.com/2010/01/bro ... trol-ectc/

The initial peak of the flash curve is very "blue". The more of the "tail" you cut off, the bluer the total result must be, if not compensated for as we do in Color Mode.

As a retired electrical engineer, now photographer full-time, I like this brochure. It was the one biggest reason that I purchased my first PCB product. It arrived today, the E640 with Power MC2 and your Vagabond Mini. I see a lot more coming this year!

I have already put it through it's paces and the unit works perfectly. Thank you for designing this product.

Tomorrow, I plan to run a color test against my SB-910's in graph form. I suspect the E640 will perform as designed.

It is refreshing to see someone (Paul) that actually knows how to tell the truth and fully understand the design decisions that go into making a quality product......and yet not gouge the customer for the performance/quality. I know of only one other US company that lives for that purpose.

With Best Regards,
Craig