Just in case anyone needs convincing what an inexact business colour balancing is, here's a graph showing the relative power across the spectrum for theoretical 5500 K and 3200 K sources, and the combination of a 5500 K source and an 85B filter, which is supposed to convert 5500 K to 3200 K. The three lines have been adjusted to meet at a relative power of 1 at 550 nm.
Helen was kind enough to loan me her two Minolta meters, so I've started doing some tests just to see how consistent flash output is.
Just figuring out how to use them, I discovered that, yes, one should really wear a black shirt when taking color readings to avoid influencing the meter.
First observation testing a small Metz 30BCT4 and a Norman LH-2 portable head with a 200C pack--well my 200C wasn't charged, so I only got a few flashes off at low power before the battery failed.
Quick observations--both were fairly close to daylight on the cool side--less than the amount of correction provided by an 81 filter, which is even weaker than the common 81A. The Metz drifted more from flash to flash, while the Norman stayed within a tighter tolerance. The lesson there is that you would have to be very sure of the tolerance and consistency of your strobe heads, film stock, processing, and viewing source, before it would be worth making adjustments of .025 CC, and I have have filters in that strength.
I'll test more rigorously with the Norman portable at different power levels when the battery is charged, and I'll also test my Norman studio heads when I have some time to set them up.
an interesting thread, but do colour meters actually get much use nowadays? why? how? where?
I'm shooting some 8x10" Polaroids under window light, so I had another chance to test the meters, and I threw my simple Gossen Sixticolor into the mix, which only reads red/blue, so it can't handle fluorescents, and it doesn't work terribly well in low light, so it's not that great for tungsten.
Well the first shot revealed that I needed a warming filter, so it seemed like a good situation to compare the three meters, though of course I could have made the correction from looking at the Polaroid itself.
First off, the Minolta IIIF is more sensitive than the others. I could get a reasonable reading from the subject position, maybe 8 feet from the window. The Minolta II and Sixticolor required that I go up to the window, and it could be that the light is bluer 8 feet away than it is right there, due to reflections in the room.
All three gave me about the same reading calling for something in the range of 81, 81A, or 81B, and it could be different depending on how precisely I directed the sensor. The conclusion might be that there is no meter that can tell you precisely whether you need an 81, 81A, or 81B, because there are just too many variables involved in the process, but it does seem informative to have some readings to base a judgment on.
As to the question of why one might want to use a color meter, I think they get the most use in mixed lighting where you have the possibility of gelling all the lights to the same color balance, or making multiple exposures with different filtration on the lens for each light source, as is often done for architectural interior photography.
Stobes can vary widely in color depending on the age of the flash tube. Also, any time you modify the lighting with a softbox, umbrella, bounce panel, etc., it will change the color of the light. The older the softbox, the warmer the light.
In the studio where I worked, we used to use strips of Rosco gels (close to, not touching) over the flashtubes to correct the color to within +- 50 degrees Kelvin on the meter. There usually was quite a bit of difference between modified and unmodified light sources.
I just had time to try another test just using the Norman LH2 heads that I keep on my copy stand most of the time.
Adjusting the strobe power from 50 to 100 to 200 W-s, there was no significant difference in color temperature from one setting to the next--at most 10 degrees K, which is within the range of variation from flash to flash on a single setting. This is as it should be, since in theory the flash output is regulated by changing only the duration.
On the copy stand I use the heads with 5" reflectors that have an opal glass diffuser and a very uncalibrated white handkerchief over each head, and the color temperature is 5480-90K--almost exactly what it should be. If I remove the reflectors, the temperature of the flashtube is a little on the blue side 5950K--enough for the IIIF to recommend an 81A.
I'll maybe bring an old thread alive.
Does anybody have experience with Kenko KCM-3100 and Sekonic Prodigi Color C-500. My Gossen 3F died during the trip to Iceland and I don't want to buy same. It has very poor construction for heavy outside use. My lost contact with display and after dismantling I'm not sure I'd like to go back to Iceland with the same color meter construction.