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SYNOPSIS
Some of my modifiers produce quite noticeable color shifts. Two lights in color-critical use like tabletop can create havoc that post cannot repair. I finally had the time, fortitude and apparatus to conduct a thorough test.
EQUIPMENT
Subject was a Profoto D4 1200 and attached Acute/D4 head, with measurements made by my newly acquired Sekonic Prodigi C-500 (flash color meter). This meter is a great tool, and made the test practical. I also queued some modifiers (Profoto brand unless otherwise noted).
SETUP
Test space was a large room of 2000 square feet, neutral in color, with 12' ceilings. I kept the rig away from all walls, furniture, and myself, to minimize color contamination. Office lights were extinguished. Meter was mounted statically at 3m from the light source for pack testing, and 1.5m for modifier testing.
METHOD
I was pleased to observe little variation of color temperature from the test rig: at a given energy setting, ±10K. The meter has readability of 10K. In most cases, I was satisfied to take the median of 3-5 measurements, pausing about three seconds between firings. Table 1 shows twelve measurements (sorted) for D4 Energy Setting 4.
THE TESTING
First order of business was pack testing. Each whole Energy Setting (3 through 10) was selected on the D4 at two different Shutter Speeds selected on the meter. With multiple firings at each setting, this test took awhile. Modifier used was the Zoom reflector @ position 4 to minimize stray light. Results appear in Table 2.
Second order of business was modifier testing. The Energy Setting was 4, except 6 for ProBox. The Zoom reflector was used when applicable. Again, multiple measurements were taken to determine the median. Results appear in Table 3.
COMMENTS
I have no grand conclusion, although the test confirms the fickle nature of color. When multiple light sources are present, including those from Nature, the task of keeping critical balance is a real chore. Random comments follow.
D4 is spec'ed to ±150K, and mine barely makes the grade. That the color shift is not monotonic over the energy range is surprising. Not surprising to me was the effect of shutter speed on color temp. I included that dimension knowing the trailing tail of light emission was not going to make the 1/500s cut-off at the highest energy setting. The trailing light is evidently cooler in Kelvin (red shifted).
The D4 is very consistent at a given energy setting. On the first firing at a new setting, however, the color temperature is occasionally off-base - even by 100K. There is an argument for the Pro-8 (okay, an expensive argument) with ±50K over most of its energy range.
I used the cordless trigger mode of the Sekonic, and one small unknown is the algorithm it uses to commence the measurement. If the leading portion of the flash emission is truncated, correlation between lights as recorded by the camera sensor may be affected.
I was pleased to see the Profoto grid having virtually no effect. The ProBox was even worst than I expected: additionally, it eats photons like no tomorrow. The Photoflex LitePanel diffuser is even more blue than I thought in bounce mode (my main use).
Perhaps most interesting is the white Chimera softbox (medium Super Pro Plus). The interior is clearly blue-shifting to counteract the yellow tint of the two diffusers. In a separate test, I determined the material of the inner one is -200K, and that of the outer is -100K. Situated within the blueish SB, the mechanics of color mixing is nontrivial. I often omitted one or other diffuser for light shaping, but on finding these chromatic implications, I won't be so cavalier.
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Profoto's standard dome is frosted, but they also have clear domes with and without the coatings.