Tedcritch Loc: Lexington, KY

Is there a way to verify a light meter is indicating in line with an accepted standard?

BebuLamar

What kind of light meter? If it's a true light meter (not an exposure meter) then you can send it out for calibration with an NIST certificate.

jamesl Loc: Pennsylvania

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You can use an 18% gray card to check the accuracy of the meter.

BebuLamar

How?

User ID

Yes, there is a way. But theres no ultimate way to confirm that the test procedure or test device is in line with an accepted standard. It like a hall of mirrors.

BebuLamar

Unlike light meter the exposure meter can be calibrated to different standards. You need to know the K factor for reflected meter or the C factor for incident meter. For a meter that is built in to a camera you also need to know the weighted pattern. For the Evaluative or Matrix meter you wouldn't know exactly how they work as no manufacturers publish details information on those.

jamesl Loc: Pennsylvania

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Put an 18% gray card in the same light as the subject you want to shoot. Fill the frame with the gray card and take your meter reading, set the exposure and take a shot of the card. View the shot on the back of the camera and look at the histogram. A properly exposed 18% gray card should show a spike in the center of the histogram (value 128). If the spike is left of center the shot is underexposed, if the spike is right of center it is overexposed. If the spike is in the center the exposure is correct.

BebuLamar

If the meter is off and the ISO rating is off or the shutter speed is off they can cancel each other out.

MJPerini

Well, the first thing to determine is if you are "In the Ball Park"
Go out on a bright sunny day, to a location with some trees & a blue sky
I'd set Base Iso, and the sunny 16 rule should apply. Say your Base Iso is 200, Take a picture (manual Mode) at 1/200 @ F 16 (or 1/400@ f/11 etc)
PS, sun at your back at first, for the simplest test
Then see what your meter reads. You could aim it at a gray card as suggested above, or if it is an incident meter just use that. Then take a few other pictures using the exposure meter and the camera meter in turns.
Shooting JPEGs would be fine so no processing skews the test
You can have the meter calibrated if you like, but that costs money.
You do not mention which meter you have or how & why you intend to use it.
I would suggest going to the Sekonic site and view a couple videos on how to use a meter.
In the right hands a good meter is a powerful and creative tool, for not just exposure, but lighting ratios both in the studio and outdoors for determining the brightness range of the scene, or integrating flash ( if the meter supports that.
Having said all that, any modern in camera meter can be used to get very good results, whereas exposure meters have a learning curve. WHERE you point any meter makes a difference, but where to point it requires a bit of knowledge.
The Cinema industry mostly uses light meters and mostly incident meters because scenes have to match, and to achieve the artistic intent .
Just try the "Ball Park Test" first. And once you determine that, ask a more specific question.
Good Luck

jamesl Loc: Pennsylvania

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That might be a possibility, but the odds on them being off by exactly enough to cancel each other out are probably slim. Under normal circumstances, the method I described will give proper exposure and show if the metering is off or not.

selmslie Loc: Fernandina Beach, FL, USA

The simplest way is to set your camera to spot meter a blank screen using manual focus, close to the screen and focused on infinity. Note the recommended ISO/aperture/shutter speed combination. Modern digital cameras are very accurate and precise.

Then point your other meter close to the same screen and set to the same ISO/aperture/shutter speed combination. The meter's over or under exposure will tell you how closely they agree.

User ID

That will simply maintain whatever variance is present. Beats me why Hawgsters think theres majic in gray cardboard.

User ID

Its majical thinking. Its the very foundation of UHH Sacred Traditions and Mythology. Were each and every element of your imaging to be functioning perfectly, which acoarst it is NOT, then you meter on gray cardboard and your system renders it as gray cardboad. EZPZ !!!

jlg1000 Loc: Uruguay / South America

Calibrating an instrument means a statistical procedure in which it is compared to an instrument of higher accuracy and which is traceable to a standard.

The camera is not such thing, it has many more sources of inaccuracy like shutter speed, iso and aperture, plus in camera processing.

Therefore, as some pointed out, if it is a light meter - aka luxmeter - then NIST is the solution (for a fee, of course)

Tedcritch Loc: Lexington, KY

MJprini,
Thank you for your thoughtful and in depth comments on meter testing. I will try your approach.
As to my meter and my motive, meter is a Goshen Luna-pro which I purchased via eBay and just want to determine its flaws ,if they exist so I can adjust camera settings to avoid wasting film and process costs which are getting higher by the day . I’m using a Kowa 6 that I really like and have not used for quite some time.
As you know older shutters can be a little erratic at times.
Again, thank you