Right. Post 17, which I was responding to, didn't seem to even imply sample variance or QC variance; It was comparing meter brands. Compariong meter brands is probably too generic for a meaningful discussion.
,,.
Brian - this has nothing to do with meter to meter variation in terms of manufacturer quality control. I've had a number of unmodified Pentax spot meters which identically matched over their full range, and even precisely matched the response of a Minolta Spotmeter F. But the Zone VI modification was exactly that - an internal modification to render a different kind of spectral response. Some people liked it, some didn't. Those can still be serviced by Richard Ritter; but otherwise, they are an evolutionary dead end.
I actually did an extensive series of tests of several spotmeters' spectral sensitivities a few years ago. There were pretty significant differences, especially under incandescent light sources, which have a lot of IR in them.
With film one can only use filters to change the response: blue filter with white flash bulbs for daylight film and orange filters for tungsten film in daylight.
Now with digital cameras have the capability to set to White Balance to: Sunny Bright, Daylight, Cloudy, ... and alter the response in post processing well beyond the adjustments with film in the past. Therefore the manufacturers probably do not feel a need to supply the sensors' response curves.
Chris - In terms of methodology, I seriously question the use of that so-so LED panel for any kind of serious color value comparison.
And did you even check it's true K temp against the alleged setting or rating using a good color temp meter? Those panels can be way off at times, and rarely reach true 5500K daylight output. Generally, they don't even take into account the yellowing effect of the overlying plastic diffuser (same problem as with light boxes except for the most expensive).
But since any skewing of results seems to have affected all the meters being tested in a similar manner, that probably didn't matter so much in this particular test case. It might with respect to critical color photographic applications, if people take the trouble. The MacBeth Color Checker Chart is a wonderful tool; but colors in nature often have a mind of their own.
Per flare, one of the Zone VI modifications was to apply flat black paint internally to the housing, to reduce flare reaching the sensor. I just use a threaded on rubber lens shade, just like on a camera lens, and perhaps hand shade it too, when taking a reading. That should be routine, common sense procedure for everyone.
There is no ISO standard “K” value. Meters don’t all read the same.
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