How to test my light meter?

removed account4 · Jan 14, 2011

hi barry

i have never used the exact meter you are using, but have a lunapro sbc, and it is a great meter.
years ago mine ( really my father's ) died and it was sent back to bogen to be fixed, it cost a bunch of $$
back then, but it has been 25 years since and still working perfectly.

are you using it with the ambient dome off the sensor and using it as an ambient meter ?
fresh batteries ?

sunny 16 is a good way to measure light as oldbikerpete suggests ... but as mark also mentions in a lot of places it is sunny 11.
do the test, take notes, run some film through your camera,
and calibrate your meter as mentioned in the manual.
there should be a little screw in the back so you can change the position of the needle
once you decide if it is a little off.

good luck !
john

bestbefore1978 · Jan 14, 2011

Hi,

I've also got the Luna-Pro F, and I did need to have it recalibrated when I bought it second-hand.

The issue was nothing to do with the electronics or sensor, but the printed scale inside the rotating ISO/ASA speed dial had become misaligned by about 6 stops!

This must have happened with wear and tear and caused it to become unstuck. Got that fixed and it works fine.

Worth bearing in mind though, you wouldn't have that problem with a meter with a digital readout

pnance · Jan 14, 2011

To calibrate any meter, it must be compared with a known standard. This is what they do when you send your meter to any repair facility (or the manufacturer). So all you really need to do is compare the meter to any meter you have that you know is correct.

Where can you get, or borrow one? All you need is a device that contains a light meter and is self testing for accuracy.

Maybe this is what digital cameras are for? You can meter a scene, take an exposure and check it for correctness, and use the verified exposure to check your meter. Then you can use your meter knowing the settings are correct. Hopefully.

Paul

benjiboy · Jan 14, 2011

Hi Barry, you don't say in your post what reason you have to believe that your meter is inaccurate in the first place, are you getting poor exposures ?

Diapositivo · Jan 14, 2011

Regarding sunny f/16, I think the rule states that you use f/16 when the sun is exactly behind your subject, and the implication probably is your "flat" subject, like the façade of a building.

When the sun makes an angle with your subject (let's say 45° on one side) the you have to open more. I also find that generally speaking a clear sunny day wants 1/125 @ f/11 with 100 ISO film. If you take a picture of some tridimensional object (a face, a statue, a vase of flowers) you compensate always a bit for the part which a bit more in the shade.

I would only use f/16 if the sun really is perpendicular to the focal plane. When I measure a marble building lit by the sun I get around 1/125 @ 22 + 3/10, which make me calculate my exposition "for the highlights" exactly at f/11.

So although the sun is the same star for everybody (Italy, England, US, summer, winter, etc. a clear sun always has the same luminance) I agree that f/16 is a bit too close generally speaking.

If you use slides, I'd rather use a trustable lightmeter. For negative film outdoor in sunlight, you basically don't need a lightmeter at all (just calculate mentally and open 1 stop as a safety margin)

John Koehrer · Jan 15, 2011

If your meter is compared to another, and they don't agree. You don't know which one is wrong. Put a third meter into the mix and it may be closer to one or the other.
Now you have three variables. And 4,5, etc. eventually you may find one that matches.
If you process your own film, You just introduced several more variables into the mix.
Start with ISO, shutter accuracy(30% tolerance),aperture,water quality,temperature,developer,agitation. anything else?
You're determining a standard for YOUR particular situation. If the meter is off it doesn't matter as long as it's consistant.
Want a real test? jShoot a roll of film &* compare it to an older negative that you processed.

Green grass, Gray card, clear blue sky. Pick one.

Stivi · Feb 19, 2017

Easy peasy test - Just load a film, take pictures, have them developed, if okay, meter is okay, if not get it calibrated - why all the complications you are making my head hurt, photography is supposed to be fun !!!!!!!

markbarendt · Feb 19, 2017

Hey Stivi, welcome.

Just FYI you might check the dates on the posts.

wiltw · Feb 19, 2017

John Koehrer said:
Green grass, Gray card, clear blue sky. Pick one.

Old thread, but could not resist.

A grey card shot in unchanging light

I have not trusted green vegetation in a long time. I just measured my lawn in Jan 2017: 1/250 f/5.6 (ISO 400),
and other green trees (both deciduous and evergreen) measured within a range or -0.7EV < 1/250 f/5.6 < +1.0EV, hardly a 'reliable' set of readings.

Grey concrete is equally deceiving. In front of my home we had new concrete driveway approach poured by the city, and a new concrete walkway to the front door and driveway to the garage. 1/250 f/5.6 < 1.4EV walkway < +2.5EV driveway approach.

BTW, the incident meter reading was 1/250 f/9.5

The best of the vegetation still would have overexposed only +0.5EV (vs. incident)
The worst of the vegetation would have overexposed by +2.2EV
The best of the grey concrete would have been pretty close to incident reading.
The worst of the grey concrete would have been underexposed by -1.0EV

M Carter · Feb 19, 2017

I just don't see it as rocket science - but I can stick a 1k softbox up, mount a gray card to a stand, and put the camera on a tripod, I know some folks have to make do with shade and whatnot. My gray card is matte and reasonably even unless you really jack with the angle. I just keep it flat to camera.

I've found my phone light meter app, Minolta Spotmeter F, and more modern film cameras to be in agreement. I do fill the frame with the cameras though, and use center or spot vs. matrix. But two 8008s, and N90s, a minolta rangefinder, Nikon and Samsung DSLRs - all seem to agree just fine.

My incident meter can vary by a half stop or so, but - nature of the beast I supposed. Point it at the camera or point it at the light, you can get some variance.

trondsi · Feb 20, 2017

I would use a test roll of slide film. Slide film will show you without any doubt if your exposures are correct. Shoot the roll in both dim light, bright light, and high contrast, and take some notes on how you used the meter (e.g. were you averaging lightest and darkest areas, or simply pointing the meter at the subject?). After doing this, you will be able to use the meter even if it is slightly inaccurate, as long as you remember how to compensate.

RalphLambrecht · Feb 20, 2017

stradibarrius said:
I have an old Gossen Luna-Pro F meter and I am trying to decide if I need to replace it.
I have tried metering a scene with different cameras and the Luna-Pro and comparing the readings but I can't seem to draw any conclusions.
I need a meter when I shot my RB67 and I am under the impression that I will get more accurate readings with a hand held meter than a TTL camera meter????

Is there a method to test the Luna-Pro that is not so complicated that I need a degree in physics to use?

I have been looking at the Gossen Digi-Pro F or the Sekonic L-308S but why spend the money if my old Luna-Pro is just as accurate? Maybe I just do not know how to use it correctly???

as long as your meter complies with 'sunny16', it's fine

nathantw · Feb 22, 2017

I'm going to go an entirely different direction from this conversation. Next to the word "UNDER" on your dial you'll see a little green line. When your meter isn't in use the needle should be right on top of the green line. If it isn't then turn the screw that's on the back of the meter until it is. There, your meter is calibrated properly. Go out and enjoy using it. Speaking of which, mine is a little off center.

To test for accuracy I know my hand is +1.5 stops in bright sunshine so I just meter my hand and make sure the meter shows +1.5 stops.

Arklatexian · Feb 23, 2017

John Koehrer said:
If your meter is compared to another, and they don't agree. You don't know which one is wrong. Put a third meter into the mix and it may be closer to one or the other.
Now you have three variables. And 4,5, etc. eventually you may find one that matches.
If you process your own film, You just introduced several more variables into the mix.
Start with ISO, shutter accuracy(30% tolerance),aperture,water quality,temperature,developer,agitation. anything else?
You're determining a standard for YOUR particular situation. If the meter is off it doesn't matter as long as it's consistant.
Want a real test? jShoot a roll of film &* compare it to an older negative that you processed.

Green grass, Gray card, clear blue sky. Pick one.

When I want to make a quick check of my Leica meter or a built-in meter I aim at fresh cut grass on a bright sunny day leaving out the sky. For black & white which is all I shoot, this works for me. If the negative test-prints correctly, the meter is working as it should.......Regards!

How to test my light meter?

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