Just as the title says, how do I accurately calibrate\determine the accuracy of a light meter.

I have a Weston Master II and I know I can set the zero point from the back, but how will I know that the number of foot candles it reports is accurate?

I can compare it to other cameras, but when I do that on the Rebel 2000 I get the same result and a different on the AE-1. So, I don't think that is a good answer.


1 Answer 1


Most calibration is done by comparing a device under test to one that's known good or by using a calibrated reference source. Many metrology labs offer this as a service, usually in ways that can be traced back to NIST or another standards organization. The cost will be many times the value of your Weston meter.

The zero point adjustment on your meter puts a mechanical offset on the needle, which makes it easy to calibrate for no light. If there's anything in the meter's electronics that's causing error, there's not going to be much you can do to adjust it other than cleaning the potentiometer surfaces.

  • \$\begingroup\$ I think it the same can be said for digital meters as well? \$\endgroup\$
    – SailorCire
    Mar 5, 2015 at 17:13
  • \$\begingroup\$ @SailorCire: Digital meters could be calibrated by embedding a table that says when the sensor reads x, the corrected value is y. Analog meters are at the mercy the electrical properties of the parts inside. \$\endgroup\$
    – Blrfl
    Mar 5, 2015 at 17:38
  • \$\begingroup\$ Correct answer. I would expect a proper calibration to cost around US $100. It's a lot like paying a plumber or mechanic: you're paying for the cost of a skilled worker's time and for a slice of the cost of all the equipment they need to do the job. Calibration equipment is expensive. A complete cal station in the lab might have hundreds of thousands of dollars worth of equipment in it. \$\endgroup\$ Mar 5, 2015 at 18:16

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