Testing the lightmeter accuracy on a 35mm camera

wiltw · Feb 11, 2022

unwantedfocus said:
Hello, as some of you know people DIY shutter speed testers, is there a equivalent to test the lightmeter in a camera? What would be the best way to go about it? I do have a digital camera and a handheld flashmate lightmeter. Also there are spotmeters and matrix like the minolta models would this be differently measured? Any suggestions would be helpful.

Aim a meter at an 18% grey card, so that the meter sees only the card. Set that exposure on the camera (whether or not the camera has a meter). Then set a target that has both black area and white areas and photograph it at that setting...should result in dense black and fairly white whites in a sllde or print.
Do the above with an in-camera meter, too, with camera close enough for the grey card to fill the frame while taking the exposure measurement.

Stephen Benskin · Feb 12, 2022

This is from Stimson, Allen, An Interpretation of Current Exposure Meter Technology, Photographic Science nd Engineering, Vol 6, Number 1, Jan-Feb 1962.

One of the more telling statements from the paper is "Among other innovations, meters will henceforth be calibrated at 4700 K instead of 2700 K to make them more accurate in daylight and eliminate the need of different tungsten speeds for most panchromatic materials." There was a period where films would have two exposure indexes: one for daylight, and one for tungsten. The change in the color temperature for calibration, split the difference between daylight and incandescence, it made neither absolutely precise and the degree depended on the spectral sensitivity of the meter's photo cell.

unwantedfocus · Feb 12, 2022

Thank you for all the amazing input. I will dig deeper.

RalphLambrecht · Feb 12, 2022

unwantedfocus said:
Hello, as some of you know people DIY shutter speed testers, is there a equivalent to test the lightmeter in a camera? What would be the best way to go about it? I do have a digital camera and a handheld flashmate lightmeter. Also there are spotmeters and matrix like the minolta models would this be differently measured? Any suggestions would be helpful.

sunny 16 is always a reasonable comparison.

Chan Tran · Feb 12, 2022

use one of these to test both the shutter speed, shutter curtain travel time and yes the meter.
https://www.flickr.com/photos/29504544@N08/6950255307

pentaxuser · Feb 12, 2022

Bill Burk said:
View attachment 298154

One of these. There’s two like it on eBay one is less than $75 free shipping, the other is like mine with the timer jimmied for about $100

Bill isn't that big yellow ball in the sky very consistent in its output as well and its free but yes, I admit, it does hide occasionally

pentaxuser

Chan Tran · Feb 12, 2022

pentaxuser said:
Bill isn't that big yellow ball in the sky very consistent in its output as well and its free but yes, I admit, it does hide occasionally

pentaxuser

For testing meter you need more than 1 standard light levels to test. Minimum 2 if not more. So using the yellow ball you only have one standard and also you don't really need a meter when shooting under that yellow ball.

Alan Edward Klein · Feb 12, 2022

wiltw said:
Aim a meter at an 18% grey card, so that the meter sees only the card. Set that exposure on the camera (whether or not the camera has a meter). Then set a target that has both black area and white areas and photograph it at that setting...should result in dense black and fairly white whites in a sllde or print.
Do the above with an in-camera meter, too, with camera close enough for the grey card to fill the frame while taking the exposure measurement.

If the shutter speed is off, you;ll be calibrating the meter incorrectly. If the developing is off, same thing. Too many variables could leave the meter calibrated incorrectly. You need an input that's reliable, a known quantity, so your meter will work with all your cameras regardless of the developing process, shutter speed, or other variables.

Bill Burk · Feb 12, 2022

I needed a reference for my SEI photometer. Although I “can” meter the surface of the sun with it, I prefer to keep my eyesight.

The interesting thing about the SEI, 100 foot lamberts is about the top of one scale and the bottom of another

Stephen Benskin · Feb 12, 2022

Don't forget Illuminance changes with the time of day, season, and latitude. Here's a page from the ANSI Exposure Guide.

You need to be realistic in your expectations. It's an exposure meter and not a photometer. Check it against another meter. What you want is repeatability and linearity. How you use the meter will most likely have a larger influence on your exposure than any discrepancy the meter may or may not have.

snusmumriken · Feb 12, 2022

Depending on the model of camera you are testing, making sure you are metering from the target area (e.g. grey card) and nothing else can be harder than it sounds. It it's a rangefinder camera, the viewfinder isn't necessarily looking where the lens is at close range. If the viewfinder is parallax-corrected as in a Leica, and you focus the lens, then the two will 'see' the same thing. But if you have to move in beyond the closest focussing distance in order to make sure the meter sees nothing more than your target, the viewfinder is no longer seeing the same as the meter.

Paul Howell · Feb 12, 2022

The safest bet is have your handheld meter tested and calibrated, most repair shops can at least test a meter, some will work on new models. The repair shop I use will test and calibrate most battery models, will repair a few. You can also down load a light meter app on your smart phone, some folks swear by a phone app, others hate them, I don't have any experience so don't know.

Stephen Benskin · Feb 12, 2022

Paul Howell said:
The safest bet is have your handheld meter tested and calibrated, most repair shops can at least test a meter, some will work on new models. The repair shop I use will test and calibrate most battery models, will repair a few. You can also down load a light meter app on your smart phone, some folks swear by a phone app, others hate them, I don't have any experience so don't know.

Best advice.

If your interest is limited to whether something isn't working correctly, bring it to someone who has the experience and the expensive test equipment (and keeps it maintained). Have it checked, then spend your time using it.

beemermark · Feb 12, 2022

Alan Edward Klein said:
So let's say the whole roll is a little dark. How much do you adjust the meter to get it to read correctly for the next roll of film? 1/3 of a stop, 1/2, a full stop? What if you made a mistake in developing in addition to the meter being off? You really need to calibrate the meter to a known and accurate input.

1/3 or 1/2 of a stop falls in to personal preference, i.e. what I think of the negatives. Once you hit a full stop or two it's pretty obvious. But shoot a roll of film of the same subject with some parts in deep shade and some in sunlight and develop the roll. Make the bracketing as wide as you want. You'll narrow down with one roll.

Sirius Glass · Feb 12, 2022

Alan Edward Klein said:
If the shutter speed is off, you;ll be calibrating the meter incorrectly. If the developing is off, same thing. Too many variables could leave the meter calibrated incorrectly. You need an input that's reliable, a known quantity, so your meter will work with all your cameras regardless of the developing process, shutter speed, or other variables.

Which is why I keep harping on having the meters calibrated and the cameras adjusted. Having a so called EI means nothing if the camera is off.

Bill Burk · Feb 12, 2022

Before going that far. Is there any reason to doubt the Sekonic? Not every light meter is in need of calibration. In an amateur world you may use your own things to pick a reference and then build off from there.

When I had a Minolta X-370 that was the most accurate shutter of my cameras so it became my reference.

I don’t normally buy Minoltas but once, when I was living in Houston, I drove down to Galveston and camped on the beach. It was a long time ago. I was on-call and carried a pager. I think the idea was that if I got beeped I would find a payphone somewhere to call the number. I befriended a family on the beach and, as people sometimes do, they told me they had a camera they didn’t need and asked me if I could I use it. I said sure I will take a look at it and followed them back to their house.

They showed me the camera, mentioned what they were hoping to get for it and I agreed. One of the things I remember is they had few working light bulbs (it illustrated for me the concept that when you’re barely making it you have priorities). It was more than the camera was worth but I didn’t need money or camera, I just wanted to do something nice for them.

I never used that camera for anything but as a reference for checking my other cameras long exposure shutter times. Eventually when I moved back to California, I put an old Omega DII on layaway using the X-370 towards the purchase. (I used that enlarger until last year’s grain focus experiments when I needed the D2 crank).

wiltw · Feb 12, 2022

Alan Edward Klein said:
If the shutter speed is off, you;ll be calibrating the meter incorrectly. If the developing is off, same thing. Too many variables could leave the meter calibrated incorrectly. You need an input that's reliable, a known quantity, so your meter will work with all your cameras regardless of the developing process, shutter speed, or other variables.

True statements. OTOH, if one sets calibration based upon inherent variability of shutter, aperture, film speed rating based upon developing 'standard' for a particular user, the entire 'system' is calibrated for consistency of results.

The best calibration check of a meter is with a 'reference standard' amount of light, with which one can validate the meter reading of shutter+aperture+ISO is the right combination, but few of us have direct access to one.

Bill Burk · Feb 12, 2022

By no means do I intend to contradict expert advice to get the meter calibrated when I advocate for the complete opposite!

Me saying to do the exact opposite of what my friends say is not the same as saying I don’t agree with them.

It’s just how I am, that I would do things my way and tell the story, even though there are better ways to go.

pentaxuser · Feb 12, 2022

Chan Tran said:
For testing meter you need more than 1 standard light levels to test. Minimum 2 if not more. So using the yellow ball you only have one standard and also you don't really need a meter when shooting under that yellow ball.

No, I agree that you do not need a meter when shooting under that yellow ball but my reference to it was as a standard and if the yellow ball dispense with the need for a meter doesn't that indicate that the rule we used called the sunny f16 is completely accurate as a light source. Don't we usually need 2 sources when the problem is the accuracy of the sources but this isn't the case with the sun. It is unfailingly accurate

pentaxuser

Bill Burk · Feb 12, 2022

By the way, a few Wratten No.96 ND filters come in handy for this. You will want 0.1 and 0.2 ND to get those third stops.

wiltw · Feb 12, 2022

pentaxuser said:
No, I agree that you do not need a meter when shooting under that yellow ball but my reference to it was as a standard and if the yellow ball dispense with the need for a meter doesn't that indicate that the rule we used called the sunny f16 is completely accurate as a light source. Don't we usually need 2 sources when the problem is the accuracy of the sources but this isn't the case with the sun. It is unfailingly accurate

pentaxuser

And in recent times, I have proven that the 'reference standard' yellow ball does not necessarily result in exactly f/16 all the time...what we THINK is 'clear blue sky' can in fact have smoke particles or even water moisture affect the brightness at ground level, yet our eye says 'clear cloudless sky'.

BrianShaw · Feb 12, 2022

wiltw said:
And in recent times, I have proven that the 'reference standard' yellow ball does not necessarily result in exactly f/16 all the time...what we THINK is 'clear blue sky' can in fact have smoke particles or even water moisture affect the brightness at ground level, yet our eye says 'clear cloudless sky'.

If one believes the tables in post #36 (which I do because it correlates with a similar table I use from an 1896 photography book), one can always be assured that the sun is approximately f/16, or less.

Sunny-16 was always intended to be, and advertised, as an approximation... a starting point, not an absolute or standard. I don't know why it all of the sudden seems to have changed in some people's mind.

Bill Burk · Feb 12, 2022

Alan Edward Klein said:
If the shutter speed is off, you;ll be calibrating the meter incorrectly. If the developing is off, same thing. Too many variables could leave the meter calibrated incorrectly. You need an input that's reliable, a known quantity, so your meter will work with all your cameras regardless of the developing process, shutter speed, or other variables.

I wanted to say you can just check things without trying to calibrate, then use the things that seem right.

Chan Tran · Feb 12, 2022

pentaxuser said:
No, I agree that you do not need a meter when shooting under that yellow ball but my reference to it was as a standard and if the yellow ball dispense with the need for a meter doesn't that indicate that the rule we used called the sunny f16 is completely accurate as a light source. Don't we usually need 2 sources when the problem is the accuracy of the sources but this isn't the case with the sun. It is unfailingly accurate

pentaxuser

2 sources is not because of the source isn't accurate. You need a bright and a dim source to properly check the meter that is the minimum. You may want to check at several brightness levels to make sure the response is linear.

BrianShaw · Feb 12, 2022

unwantedfocus in Post #1 said:
... to test the lightmeter in a camera...

Although this discussion is quite interesting (to say the least), looking at the original problem - a built-in light meter. Why not shoot a roll of film, record the exposures used, and look at the negatives? If the neg looks good then the meter is okay. If not, you can easily estimate how much the meter is off.

Testing the lightmeter accuracy on a 35mm camera

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