Monday, July 26, 2010

Strobe Power -Vs- Color

Back to a more technical topic for today's post. Earlier this year I conducted a short experiment to see just how much color shift my strobes (monolights) give as the power is varied from min to max. It is actually an important subject, as color shift is a bad thing if excessive and can go unnoticed for a long time, but then show up unexpectedly and catch you off guard (probably at the worst possible moment, like when an important client is present). This topic doesn't really fit in with anything posted lately, but the experiment was completed back in March and the data has been lying around all this time waiting to be cataloged and the results written up, so finally, here it is.

Why Should I Care About a Little Color Shift?
A little color shift is probably not a problem at all. The operative here is the word “little”. Your idea of “little” may be quite different than mine. One's definition of “little” will likely be affected by the type of photography they do and just how picky they are. You might be very picky if photographing products for a high-end catalog. The rest of us can probably tolerate more color shift and probably never even notice it. My tolerance for color shift is somewhere around 300° K (Kelvin) for critical work. Much above that and my eye says too much. Things like a hair and background lights can usually tolerate more than that without being noticed. Your tolerance may be greater or less, that is entirely up to you.

The point here is to know the characteristics of your equipment so there will be no surprises. For example, if you know that your lights shift color quite a bit between min and max power, then you will be aware of this and try to avoid lighting setups where one light gets set at high power and another at low power. This isn't something one normally encounters, but I can see where it could happen. For example, one light in a large, double diffused softbox mixed with another light using an efficient reflector.

In addition to variance from min/max power, if you use lights of different vintage, and/or make, and/or model, it is possible that they emit a different color light in addition to shifting color over their power range. It never hurts to fully know your equipment.

What is a Typical Color Shift for Monolights?
That's a very good question and one that I cannot even begin to fully answer, mostly due to lack of information, time to fully research the subject, and a way to present the information in a meaningful way.

A bit poking around on the web reveals that only some (few) manufactures publish this number. My data is published below. Please note that I am only looking at monolights, not power pack systems. A power pack system has the electronics in an external box called a power pack or generator, whereas monolights have all the electronics built into the light. Do not confuse the power pack with an external battery pack.

On the surface, it appears that typical is somewhere around +/- 200 - 300°K. However, this does not factor in the adjustment range. A light rated +/- 300°K over a 7-stop range is going to perform much better than a light rated at +/- 200°K over a 4-stop range. This may explain why some manufactures do not publish the numbers, it gets confusing.

Looking at the limited data I found, one thing becomes very clear. There are a few lights that are exceptionally good in terms of color stability. At the top of my list is the Paul C. Buf Einstein, having only +/- 50°K shift over an incredible 9-stop range! That is followed by the Photogenic Solaris with +/- 50°K shift over 6-stops and 100°K over 8-stops (I would be very happy with either of these). Honorable mention goes to Interfit with +/- 100°K over 5-stops for the low cost Stellar X and XD models.

Here is the data I found at the manufactures' websites.

+/- 300°K - Gemini 200 (200, 400 WS, 5-stop analog adjustment, AC/DC power source)
+/- 300°K - Gemini 400 (400 WS, 5-stop analog adjustment, AC/DC power source)
+/- 300°K - Gemini 250R (250 WS, 5-stop digital adjustment, AC/DC power source)
+/- 300°K - Gemini 250R (250 WS, 5-stop digital adjustment, AC/DC power source)
+/- 300°K - Gemini 500R (500 WS, 5-stop digital adjustment, AC/DC power source)
+/- 300°K - Gemini 500PRO (500 WS, 5-stop digital adjustment, AC/DC power source)
+/- 300°K - Gemini 500PRO (500 WS, 5-stop digital adjustment, AC/DC power source)
+/- 300°K - Gemini 750PRO (750 WS, 5-stop digital adjustment, AC/DC power source)
+/- 300°K - Gemini 1000PRO (1000 WS, 7-stop digital adjustment, AC/DC power source)
+/- 300°K - Gemini 1500PRO (1500 WS, 7-stop digital adjustment, AC/DC power source)

Paul C. Buf
+/- 50°K – Einstein 640 (640 WS, 9-stop digital adjustment)

+/- 300°K – EX150 MKII (150 WS, 4-stop analog adjustment)
+/- 200°K – EX300 (300 WS, 5-stop analog adjustment)
+/- 200°K – EXD200 (200 WS, 4-stop digital adjustment)
+/- 200°K – EXD400 (400 WS, 6-stop digital adjustment)
+/- 200°K – Venus (150, 300 WS, 4-stop digital adjustment)
+/- 100°K – Stellar X (150, 300, 600, 1000 WS, 5-stop analog adjustment)
+/- 100°K – Stellar XD (150, 300, 600, 1000 WS, 5-stop digital adjustment)
+/- 300°K – Stellar Xtreme (150, 300 WS, power range not specified, analog adjustment, AC/DC power)

+/- 200°K – StudioMax III Constant Color (160, 320 WS, 6-stop analog adjustment, AC/DC)
+/- 200°K – StudioMax III Constant Color (320 WS, 6-stop analog adjustment, AC/DC)
+/- 50°K full to 1/32, 6-stops
+/- 100°K full to 1/128, 8-stops
Solaris PL500DRC (500 WS, digital adjustment) & PL1000DRC (1000 WS, digital adjustment)

How Did My JTL Mobilights Perform?
Good, especially considering the less than stellar view some people have of JTL products. Above you can see the patches for the newer lights from min to max power settings at 1-stop increments. The files have all been processed using the same white balance setting of 5600°K +20 tint (slight magenta offset).

This next photo shows the patches for the older lights from min to max power settings at 1-stop increments. The files have all been processed using the same white balance setting of 5600°K +20 tint (slight magenta offset). Looks like the f/11 patch didn't quite get to f/11. Nonetheless it's the color reading we are after, not luminance.

In a nut shell, using my minimalist methods for determining color temperature, I would rate them like this:
+/- 150°K – Mobilight 300 [newer, same flash tube as the 301] (300 WS, 4-stop analog adjustment, AC/DC)
+/- 150°K – Mobilight 300 [older model] (300 WS, 5-stop analog adjustment, AC/DC)

I own four Mobilights, two sets of two from different vintage. There are some interesting differences between these two versions that I will note here. The newer version puts out a full stop more light compared to the older version. However, the older has an extra stop of adjustment range and performs better in terms of color consistency, as it has the same shift, but over a broader range. Both of them perform quite well in terms of color, better than I expected.

Here is a diagram of my test setup. The monolight is on a stand 9-1/2 ft. from the test target, which is a Lastolite 12” EZ Balance white balance disc. I took three shots at each power level to ensure consistency (which was not an issue). Between each shot, I waited about 5-seconds, which was probably not necessary, but I wanted to make sure any color shift was from the power setting and not from the capacitors not being fully charged.

For anyone interested, here are the settings to get white and the measured patch readings. The f/stop was read from the Polaris light meter and is subject to some error due to the limited resolution of the meter's graphical readout (it's good enough for normal use, but lacking for scientific measurements). You might also note that the green/magenta tint had to be tweaked a little, which suggest that there is also a minor change to the spectral envelope as the power changes, though these are small adjustments.

Mobilight 300, new version
f/16 - 5600K +20 tint, 248, 248, 248
f/11 - 5750K +21 tint, 244, 244, 244
f/8 - 5800K +24 tint, 247, 247, 247
f/5.6 - 5884K +24 tint, 252, 252, 252

Mobilight 300, old version
f/11 - 5500K +15 tint, 241, 241, 241
f/8 - 5600K +20 tint, 249, 249, 249
f/5.6 - 5600K +20 tint, 247, 248, 248
f/4 - 5700K +18 tint, 245, 245, 245
f/2.8 - 5800K +18 tint, 244, 244, 244

Coming Next
I swore off doing another series, but am considering a short series on some of the photographer's tools. It will be the kind of information that could be useful to virtually anyone who uses a camera, beginner on up. Nothing technical, just a little attention to an often overlooked topic. So next time you come to Studiography, bring a friend along. :-)

Until then...


1 comment:

  1. Gotta love the Einstein! That's my first monolight and I'd only change to another light if Paul Buff comes out with a Pack system that utilizes the same technology =D


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