Thursday, October 06, 2011

Q&A: Speedlight Color Shifts

In one of the geekier questions I have gotten in a while, reader Kevin House asked via Twitter how color temperature varies with power levels on speedlights.

The short answer is, it doesn't really vary significantly due to power level differences. But it does vary for other reasons.
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So first, the power level thing.

Color temperature variances do not seem to plague speedlights as much as they do some bigger flashes. Whatever the reason, that's one thing small-flash users don't have to sweat.

But there are cases where you can get color temperature differences. And one of those instances is actually helpful. To me, at least.

The first instance is when you are cutting it close on sync speed and working at high power. Unfortunately, this is the exact combo that comes into play when you are trying to overpower sun.

Reason is, flashes are designed to give consistent color temperature over the full span of the pulse. But this doesn't mean that to color is consistent throughout the pulse. Just that the aggregate amount of light throughout will give you something (hopefully) very close to daylight.

A pulse spikes very quickly and then trails off in a "tail," the shape of which is determined by the design of the flash and the power setting at which it is being used.

If you are shooting at max power and max sync, you may well be cutting off a meaningful amount of the energy at the tail end of the pulse. And this can cause color shifts.

Not to worry -- generally they are nothing you would notice much and are easily fixable in post.

But there is one circumstance that results in a consistent (and to me, pleasing) color shift in speedlights. As flashes age, they tend to warm up. I have old Nikon flashes that essentially have the equivalent of an 81A filter (or, say, a Rosco 08) built into them due to age.

The color shift comes from the front fresnel lens on the flash. Not sure if it is purely an aging thing, or if it has to do which how much energy the plastic has absorbed over time given the large amounts of light it transmits. But it is definitely warmer.

Whatever the case, I like it. I tend to shoot people so for me an old, warmer flash is a good thing. If I were a catalog photographer, where absolute color accuracy was very important, I probably would not be very happy about it.

But my key light tends to keep a 1/4 CTO gel on it anyway, so I left anal-retentive color accuracy at the altar a long time ago.

If any of you brainiacs know exactly why a flash warms up with age (time, transmitted energy or a combo) hit us in the comments. I'd love to know


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20 Comments:

Blogger James Bong said...

I would believe that it's absorbed energy, much like clear plastics left out in the sun change color. I work in an accelerator laboratory, and the lenses we use on cameras warm with absorbed radiation and eventually turn black. It's like having a lens with a built in ND100 filter!

October 06, 2011 9:09 AM  
Blogger yoric said...

I would think it is to do with plastic degradation as a result of the very significant UV emissions from the Xenon tube.

October 06, 2011 2:25 PM  
Blogger Gage said...

since i'm in industrial and systems engineering the geekier side of photography makes me giddy with anticipation for the next new gadget to appear or for a question like this..but about the fresnel lense..its actually the polycarbonate oxidizing from heat and small uv radiation decay. kind of like how onions are initially white and when you put them in a hot skillet they carmelize and turn brown. same effect here for the fresnel lens..of course i don't throw flashes on skillets.

October 06, 2011 2:42 PM  
Blogger Chuck said...

Many clear plastics include sulfones or urethanes in them that "yellow" with oxidation. Like many reactions, oxidation is accelerated with higher energy -- of which a flash generates in both heat and light form.

October 06, 2011 3:37 PM  
Blogger caprae said...

A friend ran his two SB-900s through an analyzer and got approximately 4950K at full power and 5200K has 1/4 power. Of course they did not match each other.

October 06, 2011 3:50 PM  
Blogger S4Steve said...

I've worked with optical plastics a lot over the years. They all share one property: They are degraded by time, temperature, and light exposure (mostly blue and UV exposure). Degradation is molecular breakdown and usually takes two forms, both of which will warm up the transmitted light. One is absorption, which hits the blue hardest and turns the material yellow. The other is scattering, which because of the physics, tends to favor blue as well, further warming transmitted light. That explains why the plastic window will contribute to warming, but I don't know if the flashtube itself warms up with age. I do know that projector lamps tend to LOSE red with age, as the gas composition changes due to leakage of small-size gas molecules. But I don't know if there's a similar effect in flashtubes that makes 'em get more friendly with age.

October 06, 2011 3:56 PM  
Blogger Roshel said...

LOVE the blog, its been a great resource for me!

October 06, 2011 5:29 PM  
Blogger Troy Piggins said...

I find I am getting warmer and more pleasing with age, so it's no surprise flashes are the same. :)

October 06, 2011 9:26 PM  
Blogger Yugo said...

The above comments strongly suggest that:
1) If you want the warmer color cast as your baseline flash, get some fresnels out of heavily-used flashguns (maybe broken ones on eBay).
2) If you want factory-fresh daylight tones, just get your fresnels replaced periodically.

October 07, 2011 10:30 AM  
Blogger JofK said...

This might help a bit with the problem? I haven't tried this one yet, but it won't cost much to try. Toothpaste to the rescue:

http://www.diyphotography.net/quick-tip-make-your-strobe-shine-with-toothpaste

October 07, 2011 2:35 PM  
Blogger "Mister Nasty Clamps" said...

David: The yellowing of the fresnel lens is something that takes place with Vivitar 285's, and I too have found this to work to my advantage when shooting people. One thing that I've done with all of my strobes is that I've measured their individual color temperatures with a white balance card and Photoshop (super easy to do), and I've then written this temperature on the back of each strobe. I then know which strobe gives the nice, warm, fuzzy light (typically for my key), and which other strobes are more suited for backlights and backgrounds.

October 09, 2011 2:48 PM  
Blogger Rey Bugia said...

This is also true for old stofens, they get warmer with age. Plus if you get one of the cheap ebay ones, they warm up a few months earlier than the original.

October 09, 2011 10:56 PM  
Blogger SuzieViews said...

Nothing to do with color shifts but not sure where's best to say how grateful I am to your fantastic blog. Have had it bookmarked for a while now & just pulled of bits & pieces telling myself I'd come & do 101 soon. After buying my 2nd SB-900 I finally had no choice! - and have had some wonderful eureka moments! THANK YOU for your generosity in sharing your no-frills / minimal lugging / down-to-earth approach and knowledge, and no mistaking God-given talent! Am now loving going through assignments.

October 10, 2011 2:12 AM  
Blogger Daniel Sullivan said...

That's why they call 'em "The Golden Years"!

October 10, 2011 8:20 AM  
Blogger Jason Anderson said...

"A pulse spikes very quickly and then trails off in a "tail," the shape of which is determined by the design of the flash and the power setting at which it is being used."

I'd love to see a post that shows this graphically...especially how the tails vary from one flash to another (say an SB800 versus a 580EX II)

October 11, 2011 12:12 AM  
Blogger Aud1073cH said...

If this warming is yellowing due to degradation of the plastic, this link may have an explanation:

http://www.vintagecomputing.com/index.php/archives/189

October 11, 2011 2:15 AM  
Blogger Wink of an eye Digital said...

Personally I believe it is overclocking your Speedlight. Everyone knows when you do this the plastic becomes 1/4 CTO or really a "BASTARD YELLOW" by the old 80's guy Dean....

October 11, 2011 9:02 PM  
Blogger Trucktographer said...

They yellow just like the composite headlights on cars and trucks.

October 19, 2011 11:43 AM  
Blogger Kike said...

The blond hair tends to get white with the years, the white flashes tends to get blonde... Benjamin Button way of life :)

March 08, 2012 8:20 AM  
Blogger lowbloodsugar said...

This reminds me of how human's retinas yellow with age. It is basically like having a CTO contact lenses on all times. It is a normally unnoticeable thing in someone's everyday life, but it is measurable and it does effect businesses that have critical color applications.

Clement

April 29, 2013 7:54 PM  

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