According to Ted Orland’s poster Photographic Truths: “No two light meters agree.” Sadly, that does seem to be pretty much the truth – unless you do something about it.
For years I had a pair of supposedly “matched” Pentax digital spot meters that were never closer than 1/3 of a stop from each other – so I had to remember which meter I used for film tests and which one I had in the field. One of these meters had an accident and got sent off to its maker for a rebuild – and came back 2/3 of a stop away from where it had been, now 1/3 higher than the meter it had been lower than! So I sent the other meter off to its maker and after two months got it back about the same as when I had sent it. Which meter was right?
I then got a dandy little “Pocket Spot” from Metered Light which sometimes agreed with one Pentax and other times, the other. The Pocket Spot was the only really “linear” meter of the three, yielding nearly identical densities on a roll of 35mm film exposed randomly on plain targets ranging in brightness from about 1 EV up to 18. Last spring I had had it with the three-meter dance and decided to finally standardize on the work of a highly competent, pro-savvy company in Hollywood. Quality Light Metric does the meter calibration for the film industry, and those folks don’t have the time to mess around with equipment that isn’t right. I sent both meters off to Hollywood.
The calibration was done in two days at substantially less cost than the “other” place, and both meters now agreed exactly with each other, and while they were still 1/3 stop different from the Pocket Spot, they were now, at least, perfectly linear. The final answer? I sent the Pocket Spot and one of the Pentaxes off to Metered Light and had them tweak the PS to match the Pentax. I now have three meters that all read the same!
My students, naturally, have all varieties of meters in their kits. Sometimes they agree with mine and sometimes not. We can tell pretty quickly whether their gear is linear, and if it is then we know they can rely on the readings, they’ll just have a different film speed than I use. But they’ll wind up with the same exposure!
If you have multiple meters and want to put an end to calibration frustration, just have them all set to the same standard, and make that your own. Contact George Milton at Quality Light Metric, 7095 Hollywood Blvd., Hollywood CA 90028. 323-467-2265. If you Google them, you’ll come up with a bunch of different addresses and phone #s. This is the current info for mail order work.