Light meters

[ChrisN]

I once read that a man with two watches can never be certain what the right time is. 😱

I have ended up with several light meters and metered cameras, each of good make and reputation, in good condition, and fitted with the correct batteries. However, they give different readings, with two stops variation between the highest and the lowest for the same evenly-lit wall. Apart from sending one to George at QLM, is there a sensible way to calibrate or determine which is closest to the mark?

If not, I guess the sensible thing is to settle on one meter, one film and a consistent developing process, learn that properly, and stop worrying about which is "right".

 

[clarence]

Shoot slides?

Clarence

 

[dmr]

I've been asking this question over and over and over on the boards now, and I keep getting non-answers, or else answers that are far beyond my capability.

What I've been doing is checking/calibrating the camera I've worked on to the one I think is closest, which is now over 20 years old and never been serviced.

The thing is, all of the cameras are obviously somewhere in the ballpark. None of them consistently overexpose or consistently underexpose. I guess I should be happy with that.

The thing that kind of frustrates me is that there's no readily available standard source of a known luminance or illuminance. The various answers I've got are along these lines:

1. Find a laboratory grade standard light source. ($$$$$$$$$$)

2. Calibrate the meter to a known-accurate one. (Suspected accurate one?) 🙂

3. Check the calibration on a clear day under "sunny 16" conditions.

4. Take bracketed exposures of gradient cards and color cards and analyze them using a densitometer.

I've been thinking of buying a new medium-grade light meter just to satisfy my curiosity as to how far off my cameras really are.

I thought I had an idea here, but I jumped to conclusion a bit too fast. They make white LEDs with certain brightness ratings, about 1 candela on up to 40 or so. However, when checking further, these ratings are the MINIMUM light output, and they will typically be some unknown value over the minimum.

There's one good article on the net somewhere on how to make a light box to test light meters, but you have to initially calibrate it using a known-accurate meter, thus the chicken-egg problem.

 

[mr_phillip]

I've been through the same experience recently. I metered against an 18% grey card and tested three handheld meters versus various in-camera meters. There was about a stop difference at the most, but they were generally within half a stop of each other.

Two of the handheld meters (a Gossen Lunasix F and a Sekonic Twinmate) have incident modes, and when used in that manner they tallied exactly every time, so I put the very slight differences between them in reflective mode down to angle-of-view.

Of the cameras I tested against the handheld meters, the most accurate systems seemed to belong to my M6 and the Voigtlander Bessaflex SLR.

 

[mbisc]

1. Find a laboratory grade standard light source. ($$$$$$$$$$)

3. Check the calibration on a clear day under "sunny 16" conditions.

That's kind of the same thing 😉

Point the lightmeter towards the clear(!) blue sky in the middle of the day with your back towards the sun, and you should exactly get "Sunny-16"