Need advice for Spotmeter calibration

[ic-racer]

Actually, checking a light meter is a service available at just about any certification lab. There are hundreds of them in the US. They won't repair or calibrate the meter; just a test against their standard.

certification and calibraton services - Google Search

 

[koraks]

certification and calibraton services - Google Search

I've checked the first five hits on that search page of US-based firms - none of them offer certification or measurement services for optical equipment, let alone light meters.
On page 2 I found the first hit that suggests they'll check instruments that measure luminance levels. You need to ask for a quote, but they appear to be targeted at business users. I have a feeling that a simple check of a light meter will cost more than a brand new, known-good light meter.

 

[Alan Edward Klein]

What about using a NEC calibration puck and monitor screen to try to calibrate your meter? Of course, it depends on the accuracy of the puck and process. But could this be done somehow?

 

[BrianShaw]

I've checked the first five hits on that search page of US-based firms - none of them offer certification or measurement services for optical equipment, let alone light meters.
On page 2 I found the first hit that suggests they'll check instruments that measure luminance levels. You need to ask for a quote, but they appear to be targeted at business users. I have a feeling that a simple check of a light meter will cost more than a brand new, known-good light meter.

Agreed. Having once used calibrated photometers and spectrophotometers for engineering/scientific research, there are plenty of labs who can and will calibrate those if they are currently "supported". That is largely what one finds with that Google search. None that I know of will bother with equipment that they not "supported", which generally includes photographic light meters wheter it's just verification or calibration. Calibration is not inexpensive nor is it a casual activity. I fear that the aged-old suggestion to have old/obselete/unsupported photographic light meters calibrated should only be repeated in the past tense.

 

[Chan Tran]

What about using a NEC calibration puck and monitor screen to try to calibrate your meter? Of course, it depends on the accuracy of the puck and process. But could this be done somehow?

That is the same as using another trusted meter to calibrate another meter. You need an instrument that you know that it is accurate.

 

[Chan Tran]

I've checked the first five hits on that search page of US-based firms - none of them offer certification or measurement services for optical equipment, let alone light meters.
On page 2 I found the first hit that suggests they'll check instruments that measure luminance levels. You need to ask for a quote, but they appear to be targeted at business users. I have a feeling that a simple check of a light meter will cost more than a brand new, known-good light meter.

Our friend Glass love to suggest sending out equipment to a pro for service and calibration something if it's done right would cost a lot more than our equipment is worth. If it's affordable I wouldn't trust it. I don't believe people can honestly making a living servicing old photographic equipment.

 

[koraks]

I don't believe people can honestly making a living servicing old photographic equipment.

I'm afraid I have some doubts as to the sustainability of that industry as well - mostly in a business sense. But maybe I'm not imaginative enough.

I suspect that the advice to "send it out to get serviced" relies on a worldview that just doesn't really match reality anymore. Either it's based on the perceptions that there's a large infrastructure of businesses that will (affordably) perform such metrology services also to private individuals. I doubt this exists in the US, and know for a fact it doesn't exist where I live. Alternatively, it might be based on experience working in industry (e.g. in an R&D environment) where one might piggy-back on umbrella contracts with a select number of B2B metrology providers for hobby projects. But such opportunities are also not as common and accessible anymore in today's business environment, with its typically much more stringent financial controls.

What about using a NEC calibration puck and monitor screen to try to calibrate your meter? Of course, it depends on the accuracy of the puck and process. But could this be done somehow?

I don't see how this would work, really. Monitor calibration involves profiling its color rendition and then having the application or operating system apply a compensation to the displayed image to compensate for the monitor's idiosyncrasies. What it does not involve, to the best of my knowledge, is calibration of absolute brightness that would be usable as a benchmark for a camera light meter.

As indicated earlier, comparison with a modern (digital) camera is the obvious way to get in the ballpark - which will by all means good enough for most purposes. It's something virtually all of us have access to.

 

[Chan Tran]

I don't see how this would work, really. Monitor calibration involves profiling its color rendition and then having the application or operating system apply a compensation to the displayed image to compensate for the monitor's idiosyncrasies. What it does not involve, to the best of my knowledge, is calibration of absolute brightness that would be usable as a benchmark for a camera light meter.

As indicated earlier, comparison with a modern (digital) camera is the obvious way to get in the ballpark - which will by all means good enough for most purposes. It's something virtually all of us have access to.

My puck can measure both luminance in Cd/m2 and Illuminance in Lux and that is similar to reflected and incident meter. For a reflected light meter calibrated to K14 it's 0.14 Cd/m2 for EV0 @ ISO100 and for an incident light meter calibrated to C250 (flat diffuser) it's 2.5 Lux for EV0 @ ISO 100.

 

[ic-racer]

First 4 hits I got with a google search:

 

[Chan Tran]

I don't see they mention exposure meter.

 

[ic-racer]

This place is about an hour from me. Last I was in contact with them was to measure my EG&G sensitometer.

 

[ic-racer]

I don't see they mention exposure meter.

Some of the labs have some information if one is unsure what a Light Meter is:

 

[Chan Tran]

I sent them an inquiry so let see what they say. I doubt that they calibrate exposure meter.

 

[Chan Tran]

What about using a NEC calibration puck and monitor screen to try to calibrate your meter? Of course, it depends on the accuracy of the puck and process. But could this be done somehow?

I have the NEC MDSVSENSOR3 puck. I just compare it to my Minolta Flashmeter VI in both reflected and incident and the differences are within a couple tenths of a stop.

 

[DREW WILEY]

These Minolta meters were calibrated to a defined industrial standard, which was precisely that same as for Pentax spot meters.
The drift of either of them was so small, that I only had to have a recalibration done about once a decade for any one of the four I had. I always kept a mint example in storage in order to double check the others in use. Never was there more than a third of a stop variance, and even if that small amount was evident over the entire scale, I had it serviced.

A lot of us used Quality Light Metric in the Hollywood area. Unfortunately, that individual is now retired. I haven't had the need to find an alternate service yet, so can't answer that question.

 

[Sirius Glass]

Please suggest one. That's what @BrianShaw was asking. The missing reality check seems more pertinent than the missing word.

I last used Quality Light Metric and calibrated all my cameras and light meters. Since then it closed its doors and the owner retired. I have not need one since, however the way I would search, as I had before, I called Samy's Camera on Fairfax and ask for their recommendation. Samy's is next to Hollywood California which still has many stores and studios supporting the movie and television industry.

 

[benjiboy]

Nothing is perfectly accurate but you should know for sure within a tolerance. You can have large or small tolerance depending how critical you are. If you have one clock and you believe your clock is absolutely accurate then you're absolutely

I h

An all I want is to tell the correct time, erhm light value

I have three 1 degree digital spot meters from different manufacturers , that when pointed at a Kodak grey card in constant daylight they all give sleigtly different readings, yet when I use the meters in the field individually with film they all give perfectly acceptable results.
In my experience comparing light meter readings is the best way to drive yourself crazy.

 

[btaylor]

The last time I had my meters calibrated I used George at Quality Light Metric who, as many have mentioned, retired a few years ago. I looked for an alternative and found SpectraCine, right here in Burbank. I haven’t needed to use them yet but it’s good to know they’re still serving the industry.

 

[DREW WILEY]

First of all, you need to use gray cards and gray scales correctly. Second, it also helps to have a consistent gray card itself. And never use a shiny one. I once measured entire stacks of them using a high end spectrophotometer, both different brands and different examples of the same alleged product number, and discovered that nearly all of them were badly off not only in the percentage of gray, but in actual alleged gray hue. The Kodak ones were the most inconsistent, probably because they had sat around on the store shelf way too long and had faded or otherwise discolored. But that's what I wanted to find out - typical real world results. For my own use, I first compare such items with my readings from the grayscale of a very carefully stored MacBeth Color Checker Chart, which has exceptional quality control.

That being said, there is no reason why identical model meters should read differently, unless of course, they're either poorly made, or else just past due for recalibration, or just plain worn out, defective battery or contact, etc.

Flare must be avoided when making a reading, just like when shooting with a camera lens. Lens hoods can similarly be used on narrow angle spot meters too.

 

[Alan Edward Klein]

That is the same as using another trusted meter to calibrate another meter. You need an instrument that you know that it is accurate.

Which of course raises the question, is my calibrated monitor really calibrated?

 

[Alan Edward Klein]

I have the NEC MDSVSENSOR3 puck. I just compare it to my Minolta Flashmeter VI in both reflected and incident and the differences are within a couple tenths of a stop.

I have the same puck (prefaced with LCD as LCD-MDSVSENSOR3) and NEC PA242W monitor. I also have a Minolta Flashmeter IIIf with a 10 degree reflective attachment plus the regular ambient bulb attachment.. How did you do the comparisons?

 

[Sirius Glass]

The last time I had my meters calibrated I used George at Quality Light Metric who, as many have mentioned, retired a few years ago. I looked for an alternative and found SpectraCine, right here in Burbank. I haven’t needed to use them yet but it’s good to know they’re still serving the industry.
View attachment 383776

Thank you for providing a list of calibration laboratories.

 

[Chan Tran]

I have the same puck (prefaced with LCD as LCD-MDSVSENSOR3) and NEC PA242W monitor. I also have a Minolta Flashmeter IIIf with a 10 degree reflective attachment plus the regular ambient bulb attachment.. How did you do the comparisons?

I assume use NEC Spectraview II. If so in the tools menu select colorimeter to check reflected light. It will display a spot for you to check on the screen and when you make the measurement check the Y in Cd/m^2 against you 10 degree spot. You can measure any spot on the wall of your house for example you don't have to measure only the spot on the screen. Use the readout and convert to EV for ISO100.
Choose in the tools menu and select ambient light measurement to check again the incident meter. It's better if you have the flat diffuser. The do the same thing convert the lux reading to EV.

For Cd/m^2 to EV log(Puck Reading / 0.14) / Log(2)= EV for ISO 100 in reflected mode
For Lux to EV Log(Puck Reading / 2.5 (3.3 for dome diffuser)) / Log 2 = EV for ISO 100 in incident mode.
Set your meter to display in EV for convenient.

 

[DREW WILEY]

Spot on the wall ? That's winging it? Show me any wall paint made of pure barium sulfate... it doesn't exist. At the very very best you have around 90% reflectance, with the remaining 10% being "off white". More likely, an alleged bright white will be around 80% at best. Using a good incident lux meter and then converting that, different story in principle; but it still leaves the other end, transmission-wise, potentially ambiguous unless proven otherwise. No thanks, I prefer a service tech and lab appropriately set up to do the job right in the first place.

 

[BrianShaw]

The last time I had my meters calibrated I used George at Quality Light Metric who, as many have mentioned, retired a few years ago. I looked for an alternative and found SpectraCine, right here in Burbank. I haven’t needed to use them yet but it’s good to know they’re still serving the industry.
View attachment 383776

Don't bother using the Service Request Form; it returns

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The resource requested could not be found on this server!

I guess a phone call might be better...