Light meter help

Philippe-Georges · Jul 16, 2024

RalphLambrecht said:
if you only have one light meter, you know exactly how to expose the film. If you have two, you can never be sure.

That is precisely why I have two exactly the same light meters and don't use them together, just one for each camera bag.
One is set without any EV correction for in the Hasselblad bag
The other one is always set with EV -2.5 stops for with the Silvestri as I always use a Center-Filter on the Super-Angulons and I use to forget that compensation.
AND avoiding to have to transfer the meter from one bag to another as I forgot too many times to do that and got into trouble...

I never ever use these light meters side by side, why would I?

So, having two (the very same-) light meters is simply practical, in my instance although...

BTW, when I compared, out of curiosity, these two light meters, they hardly derogated by only 1/10 of a stop (and then only under LED light) which is negligible!
I have to admit that I counted on Gossen's Deutsch Gründlichkeit for that...

PS: the DigiproF uses only one simple and easy to find AA battery, so if you forget to bring a spare one...

foc · Jul 16, 2024

beemermark said:
I have numerous cameras and also a lot of meters. They never agree with each other.

Just like people..........

Sirius Glass · Jul 17, 2024

Marco Gilardetti said:
It's not necessarily so. Light meters, especially "vintage" or "simple" ones, are not really linear. They once used to have a pair of calibrating points in order to fit their response curve curve to a line as best as possible, but as far as I know in all cases there are ranges in which they are quite precise and other ranges in which they are less precise. Even by sending both to calibration, perhaps they will end up marking the same light value in some ranges, but would mark disagreeing values in another range.

Again, not necessarily. Personally, I would rather pick up the one which behaves better under difficult light conditions (cloudy / night). When it's sunny, a light meter is not even really needed.

The lab I sent my light meters to, including non linear old ones, adjusted the non lineararites to be as straight as possible across each's complete range.

Marco Gilardetti · Jul 18, 2024

Mine says that, especially with "vintage" equipment, this is in most cases not feasible with the desired/expected accuracy, and that a more or less good approximation has to be accepted.

BrianShaw · Jul 18, 2024

Sirius Glass said:
The lab I sent my light meters to, including non linear old ones, adjusted the non lineararites to be as straight as possible across each's complete range.

Did your lab provide a calibration curve, or is that being inferred from the reputation/quality of the service provider? The reason I ask is because its my understandning that adjustmentn is generally done at a couple of points, the extremes of the range perhaps, and the rest falls as it may. Maybe I'm not fully informed, and maybe past experiences have made me just a bit less trusting of "trust me" situations with repairs/calibrations.

In the distant past I worked with lab-grade photo-spectrometers and when recalibrated we go got certification certificates/stickers and detailed curves to validate the precision/accuracy. While relying on reputation is generally good enough, seeing the detailed curves really helped understand any variances that existed.

Sirius Glass · Jul 18, 2024

BrianShaw said:
Did your lab provide a calibration curve, or is that being inferred from the reputation/quality of the service provider? The reason I ask is because its my understandning that adjustmentn is generally done at a couple of points, the extremes of the range perhaps, and the rest falls as it may. Maybe I'm not fully informed, and maybe past experiences have made me just a bit less trusting of "trust me" situations with repairs/calibrations.

In the distant past I worked with lab-grade photo-spectrometers and when recalibrated we go got certification certificates/stickers and detailed curves to validate the precision/accuracy. While relying on reputation is generally good enough, seeing the detailed curves really helped understand any variances that existed.

Yes, the adjustments were multipoint and one meter he redid for free almost a year later. He would provide those certifications if requested. He was George Milton of Quality Light Metric, the big shot Hollywood go to guy that Samy's used and he retired a few years ago. Samy's has someone else they use, but I have not used them yet.

BrianShaw · Jul 18, 2024

Sirius Glass said:
Yes, the adjustments were multipoint and one meter he redid for free almost a year later. He would provide those certifications if requested. He was George Milton of Quality Light Metric, the big shot Hollywood go to guy that Samy's used and he retired a few years ago. Samy's has someone else they use, but I have not used them yet.

In fewer words... no. That's okay... I, too, knew George...

Chan Tran · Jul 19, 2024

You can't do a multi point calibratoin unless the meter has the ability to do so. Unless the meter is calibrated in software I don't think any meter is capable of calibration that way.

Alan Edward Klein · Jul 19, 2024

Chan Tran said:
You can't do a multi point calibratoin unless the meter has the ability to do so. Unless the meter is calibrated in software I don't think any meter is capable of calibration that way.

What's multipoint calibration?

BrianShaw · Jul 19, 2024

Alan Edward Klein said:
What's multipoint calibration?

Zero or span adjustment (one point)
Zero and span adjustment (two points)
A multipoint adjustment (three to eleven points)

For example:

I'm assuming that you aren't interested enough to wade through this, but the pictures may help for context of an in-camera multipoint metering system. In case you are interested:

https://patentimages.storage.googleapis.com/f3/52/a1/b9af987ee15c6c/US6982744.pdf

Alan Edward Klein · Jul 20, 2024

BrianShaw said:
Zero or span adjustment (one point)

Zero and span adjustment (two points)

A multipoint adjustment (three to eleven points)

For example:
View attachment 374303

I'm assuming that you aren't interested enough to wade through this, but the pictures may help for context of an in-camera multipoint metering system. In case you are interested:

https://patentimages.storage.googleapis.com/f3/52/a1/b9af987ee15c6c/US6982744.pdf

Brian, That's what I thought. When I was younger working as a tech, I always checked the instrument's scale's middle, bottom and top when calibrating. If you only check one point, you may find the instrument isn't linear and will be a lot different in other spots. If they aren't you have to estimate a mean average and calibrate to it.

For example, if you use daylight and adjust to f/16, you may find that the meter is then off at the more open end of let;s say f/8 or f/2.8. So you ought to check various light conditions unless you're sure the meter is linear. Are light meters linear?

Chan Tran · Jul 20, 2024

Alan Edward Klein said:
Brian, That's what I thought. When I was younger working as a tech, I always checked the instrument's scale's middle, bottom and top when calibrating. If you only check one point, you may find the instrument isn't linear and will be a lot different in other spots. If they aren't you have to estimate a mean average and calibrate to it.

For example, if you use daylight and adjust to f/16, you may find that the meter is then off at the more open end of let;s say f/8 or f/2.8. So you ought to check various light conditions unless you're sure the meter is linear. Are light meters linear?

You can check at mulit point to veryfy the linearity of your instrument but I don't think any non digital exposure meter can be calibrate with multipoint. If the sensor loses its linearity then that's it.

MattKing · Jul 20, 2024

With non-digital instruments, one can deal with non-linearity by customizing the reference points on a scale.
Think of meters with moving needles, and a reference scale behind the meter where the reference points on it are not spaced equally.

Chan Tran · Jul 20, 2024

MattKing said:
With non-digital instruments, one can deal with non-linearity by customizing the reference points on a scale.
Think of meters with moving needles, and a reference scale behind the meter where the reference points on it are not spaced equally.

Yeah you redraw the scale.

Light meter help

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