Not matching light meter values

[Alan Edward Klein]

No doubt; a very true statement about the importance to correctly use meters, especially when of different designs. But don't assume that only one is off as both could be off by 1/4 stop in the same direction.

Case in point: I happily used Weston meters in a vertical position until I compared the readings with a "better and more modern" meter. Then discoverred that the corrrect position fo using a Weson meter is in the horizontal postiion, and a map of the acceptance pattern proved that my "incorrect reading" were because of that. Using that specific Weston meter became much more in agreement with the "modern meter" when the erroneous use was corrected. Truth be told, though... the minor difference in exposure recommendation was rather insignificant to practical image making.

I have the same problem you do, Brian, with my meters. Aiming them correctly is the problem. A little this way or that, and the readings are different. That could be the OP's problems as well.

 

[BrianShaw]

I said in the earlier post that he should have the first calibrated to an accurate standard. Then calibrate the others to the first.

But how or by whom? That recommendation is theoretically correct but may not be practical, although it would be a tad more correct to say that both should be directly calibrated to a known and accepted standard. Who is still calibrating old meters... nobody that I know of.

 

[BrianShaw]

I have the same problem you do, Brian, with my meters. Aiming them correctly is the problem. A little this way or that, and the readings are different. That could be the OP's problems as well.

I have an additional problem, Alan; I can't type very good, as my spelling seems to indicate. LOL

 

[Chan Tran]

If there's no way to calibrate, then he'll have to offset the ISO setting by the amount of error in the meter's reading. He should check dark, medium, and light conditions to verify the readings are linear. You could get accurate readings under one lighting condition but not another.

I think all light meters must be able to calibrate some how but I wouldn't know how to access the calibration adjustments. Also some newer meter would be calibrated via software and thus you need the software which is not available to the user.

 

[BrianShaw]

I think all light meters must be able to calibrate some how but I wouldn't know how to access the calibration adjustments. Also some newer meter would be calibrated via software and thus you need the software which is not available to the user.

Plus, you'd need a calibrated light source... something most of use will never have. Calibration is a laboratory procedure.

It's a fair assumptionn that all meters are adjustable and were either directly calibrated or verified against a calibrated meter at some point in their original life. Getting details for repair/calibration of light meters is not nearly as easy as getting similar information about cameras and lenses.

That's why I always promote the practical approach of testing with actual photographic images and stipulating that if the image is good then the meter is good enough too. (Others may not agree...)

 

[Chan Tran]

Plus, you'd need a calibrated light source... something most of use will never have. Calibration is a laboratory procedure.

It's a fair assumptionn that all meters are adjustable and were either directly calibrated or verified against a calibrated meter at some point in their original life. Getting details for repair/calibration of light meters is not nearly as easy as getting similar information about cameras and lenses.

That's why I always promote the practical approach of testing with actual photographic images and stipulating that if the image is good then the meter is good enough too. (Others may not agree...)

This I don't agree. If the images are good the meter may not be good and in many cases the meters are good but the images are not. I do want good meters which are accurate to the standard that they are calibrated by. I will be reponsible for making my images good.

 

[BrianShaw]

I understand you. Perhaps I should have used the word “exposure” rather than “image”. But some might quibble that also.

 

[Chan Tran]

I understand you. Perhaps I should have used the word “exposure” rather than “image”. But some might quibble that also.

By good I do mean good exposure not composition etc..

 

[Bill Burk]

No doubt; a very true statement about the importance to correctly use meters, especially when of different designs. But don't assume that only one is off as both could be off by 1/4 stop in the same direction.

Case in point about correct usage: I happily used Weston meters in a vertical position until I compared the readings with a "better and more modern" meter. Then discoverred that the corrrect position fo using a Weson meter is in the horizontal postiion, and a map of the acceptance pattern proved that my "incorrect reading" were because of that. Using that specific Weston meter became much more in agreement with the "modern meter" when the erroneous use was corrected. Truth be told, though... the minor difference in exposure recommendation was rather insignificant to practical image making.

I have not confirmed that there is a “right way to hold”. I think they should read the same. Note: there are balances on the D'Arsonval movement that allow zeroing horizontal, vertical and flat. Once the movement is balanced in three dimensions there is a front and back zero adjust, the goal would be to have the back side adjuster in the middle of its range and use the front adjuster to zero.

The calibration would be to use a light standard and check the needle indicates the standard value.

Weston are hard to adjust upwards, and I believe the ones I have all read low.

You can adjust down by inserting a cardboard cat-eye cutout. If there is one already you can remove it to increase the reading. But mostly you’re stuck if it reads low.

Once you get the low readings set, you could drill or plug holes in the high slide to adjust the high readings.

 

[Bill Burk]

I really want to be able to evaluate a scene (Or a trans-illuminated panel) in candles per square foot. My calibration notes are in terms of candles per square foot actual vs what the meter indicates. I have one meter I trust: Sekonic L-758DR and an old gray Gossen Luna Pro keeps up pretty well with it.

So day-to-day knock around get the setup together with the Luna Pro and then check with the Sekonic. Those readings become my actual light and notes include the source, filters, attenuators, and distance.

Now I switch in the Weston and lose my mind because I can’t get 32 candles per square foot to read 32

 

[Philippe-Georges]

I wonder if it ever would be possible to match these two so different light meters.

The two Sekonic meters the OP is talking about have two absolutely different technology, the measuring cells having different sensitivity, not only for intensity but for colour too, and one is operating with a battery the other isn't.

Not to mention the reading screen: LCD versus an analogue pointer.
When reading an analogue pointer, the position of the eye is important, an oblique view can easily make a difference of 1/3 F stop.

 

[Alan Edward Klein]

Here is Google search for calibration. Probably too expensive.

light meter calibration services - Google Search

Individual companies:

Light Meter Calibration

Transcat offers light meter calibration and photometric calibration services for AEMC, Extech, VWR, Sperry & Fluke photometers. Free calibration quotes!

www.transcat.com

Light Meter Calibration Services | ILT

At International Light, we offer ISO17025 Accredited Calibration Services for a wide array of light measurement devices.

www.internationallight.com

Light Meter Calibrations

Applied Technical Services offers light meter calibrations that are traceable to the National Institute of Standards & Technology (NIST).

atslab.com

 

[MattKing]

This is intended to be helpful, not confrontational.
The other type of "calibration" is the one you perform.
Take two meters - one that gives you good results over a wide range of light levels, and the other that you need to check.
Also take one sheet of paper and one pen.
Compare the readings between the two meters over a wide range of light levels and use the pen and paper to note down any differences. Convert those notes into a table, and then use that table in conjunction with the second meter.
It isn't fast or convenient, but it is functional.

 

[BrianShaw]

That's definitely not confrontational, Matt. That's the practical approach for a photographer using vintage light meters. What you suggest is a reasonable approach but not what I'd really consider "calibration": it's more of an alignment with an acceptable metering device. Given the amount of latitude across the entire photographic chain, that is generally good enough. The use of a metrology lab, as seems to have been suggested earlier, and the quest for exact, accurate, precise, etc. light readings, is really much more effort than it would be worth

Didn't Aristotle, Shakespeare and Voltaire have something to say on that topic?

 

[Bill Burk]

Writing down the deviation between actual light and meter reading is the third step, after cleaning, balancing and zeroing.

I dream of a meter where readings match full scale high and low.

Next I dream of doing that with tungsten driven / filtered to 4700K.

And then to be able to do it for all the Westons

 

[Fatih Ayoglu]

So…
The gray card has arrived. I have done the test I’ve mentioned earlier. Read incident light with both Sekonic and then reflected light with Pentax, shot with my digital camera. The aim was to have a peak in the middle of the levels tool and when shooting I made sure I use something like f/8 and fill the entire frame with the gray card.
The camera and the digital Sekonic is more or less the same. Old Sekonic is 1/3 to 1/2 lower. But more interestingly, Pentax Digital Spotmeter was always 1 stop darker, consistently. I’ve made several readings, several tests, made sure the card is angled, like on Kodak instruction sheet. The test was done by the window looking North, it was a cloudy day, typical British weather. So now I have a bigger problem as the spotmeter is 1EV off. ????

 

[BrianShaw]

What a predicament!

I compared incident light readings between 2 of my meters, a Sekonic L-558 and Gossen LunaPro SBC and found a 1/3 stop discrepancy, with the Gossen being lower. Both give me excellent images so I feel okay about using either indiscriminately.

But I’m not going to spot meter a gtay card with the Sekonic. Couldn’t bear getting bad news like you did.

Hope you figure it out soon!

 

[Fatih Ayoglu]

What a predicament!

I compared incident light readings between 2 of my meters, a Sekonic L-558 and Gossen LunaPro SBC and found a 1/3 stop discrepancy, with the Gossen being lower. Both give me excellent images so I feel okay about using either indiscriminately.

But I’m not going to spot meter a gtay card with the Sekonic. Couldn’t bear getting bad news like you did.

Hope you figure it out soon!

Precisely, I can live with 1/3 to 1/2 EV difference between 2 meters, that can be corrected with printing easily. However I was shocked to see the spot meter gave me always 1 stop darker images. Over the next days, I’ll do the same test outside, in the garden to see what I achieve. Also will do a film test, shoot the same scene with 3 meter readings to see which one is/seems better…

 

[Philippe-Georges]

I never could match two light meters of different make and type, whatever I tried.
So I got rid of a few and bought two exactly the same meters by brand and type (and even built version): now these are two Gossen Digipro F.
These two match with deviation of hardly 1/10th of a stop, in ambient natural aswel as in artificial light AND flash, by incident - and reflecting metering.
When you take off the Digipro's little diffusing dome, which is held by a bayonet fitting, then a meniscus lens is revealed and the meter can be used as a reflective meter, the way as the good old Lunasix did.

PS: After 40 years of professional photography I can't live with only one lightmeter...

 

[Bill Burk]

If you fill frame with gray card and shoot the incident meter reading settings. Then shoot the card on automatic. Do the two digital shots match?

 

[Fatih Ayoglu]

If you fill frame with gray card and shoot the incident meter reading settings. Then shoot the card on automatic. Do the two digital shots match?

Yes, so

• automatic was 1/12 f/8
• Digital Sekonic 1/15 f/8
• Analog Sekonic 1/20 f/8
• Pentax 1/24 f/8

This was in the room, next to a window looking North, on a cloudy day. ISO was 200

 

[Bill Burk]

Which exposure put the histogram where you expected?

 

[RalphLambrecht]

Which exposure put the histogram where you expected?

I'll stick to the sun; the only consistent light source we all have access to.

 

[Fatih Ayoglu]

Which exposure put the histogram where you expected?

Camera, right in the middle of the level curve. Digital Sekonic is not too far of, Old Sekonic is 1/3 EV darker.

Pentax Digital Spotmeter which I thought would be the most accurate is 1 EV darker, which is now a bigger problem for me.

 

[Fatih Ayoglu]

I'll stick to the sun; the only consistent light source we all have access to.

Sure but not in UK. It is constantly cloudy and grey. Yes I know it is bit like a huge diffuser but I am not good at calculating that.