Need advice for Spotmeter calibration

[wiltw]

One would suspect that the meter manufacturer provides a repair/calibration adjustment service for the respective exposure meter.

• Konica Minolta for Minolta or Konica brand meter
• Sekonic for Sekonic meters

 

[DREW WILEY]

Not necessarily. Besides, manufacturers themselves might not respond to used equipment past a certain point. Many of the best meters are no longer being made, but potentially still have a longer useful lifetime. Some might have they own contracted repair facility, some might not. It all depends.

 

[Chan Tran]

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.

It doesn't have to have 100% reflectance. Any reflectance will do. Just need an evenly lit surface that is large enough because the angle of acceptance of the puck is quite large.

 

[DREW WILEY]

I'm just suspicious of any application like that, Chan, at least in terms of doing things correctly in the manner a properly equipped technician makes his living doing. Even if one has only a single reference meter on hand, by which to check his other meters and potentially tweak their readings, that meter itself should at least be professionally checked or serviced if there is any doubt. With a kind of computer system and screen feedback, you've got all kinds of intermediate hurdles which have to be taken for granted, just like in TTL metering, but worse. Being half a stop off with some black and white films might not be earth-shattering; but it would be intolerable in the world of chrome film exposure, or even in critical lab applications of b&w films.

 

[Alan Edward Klein]

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.

Chan's recommendation is a comparison between the NEC puck and the meter. If they match, then the meter is calibrated. The amount of reflectance doesn't matter since it will be the same subject measurement for both instuments. At least that;s my understanding.

 

[Alan Edward Klein]

I'm just suspicious of any application like that, Chan, at least in terms of doing things correctly in the manner a properly equipped technician makes his living doing. Even if one has only a single reference meter on hand, by which to check his other meters and potentially tweak their readings, that meter itself should at least be professionally checked or serviced if there is any doubt. With a kind of computer system and screen feedback, you've got all kinds of intermediate hurdles which have to be taken for granted, just like in TTL metering, but worse. Being half a stop off with some black and white films might not be earth-shattering; but it would be intolerable in the world of chrome film exposure, or even in critical lab applications of b&w films.

Of course this raises the issue is whether the NEC puck used for calibrating monitors is calibrated. NEC recommends calibrating your monitor every month or so. But I don;t know if they have a way of verifying and calibrating the puck

 

[wiltw]

Not necessarily. Besides, manufacturers themselves might not respond to used equipment past a certain point. Many of the best meters are no longer being made, but potentially still have a longer useful lifetime. Some might have they own contracted repair facility, some might not. It all depends.

Well, Konica Minolta handles only NON-photographic light meters.

Sekonic seems to have photographic meter service (with calibration adjustment). Information for those in the USA...

Service & Repairs​

Sekonic products purchased from or distributed by MAC Group may be sent through your local dealer or directly to our national service headquarters or other authorized service center. International Shipping is not covered under warranty service.​

​

Ship prepaid and insured to:​

​

Sekonic Service Department​

MAC Group​

75 Virginia Road​

North White Plains, NY 10603​

Fax: 800-321-2205​

Email: service@sekonic.com​

parts@sekonic.com​

​

And the web page has a Q&A section which reads...

​

Who should I ask for checkup and calibration?​

Sekonic has authorized distributors in each country for checkup and calibration.​

Please get in touch with a distributor in your country.​

​

I found a calibration service, International Light Technologies, (978) 818-6180, whose website also specifically mentions brands inclusive of photographic meters, although non-photographic meters are made by these companies...

​

In addition to offering accredited calibration for our own meters, we also calibrate meters from other manufacturers including the following light meter manufacturers:​

​

Avantes, Cooke, Daavlin, Delta OHM , Dymax, EIT, Excelitas, Exfos, Extech, Fluke, G&R Labs, Gigahertz-Optik, Greenlee, Gossen, Hamamatsu, Honle, Jelight, Konica Minolta, Lesco, Linshang, National Biological, OAI, Ocean Optics, Omega Engineering, Omnicure, Opsytec Dr. Grobel, Optimum, Sky Instruments, Solarmeter, Spectral Products, Sekonic, Spectroline, Spectronics, Sper Scientific, UDT, UV Power, UV Process Supply, Testo, UVX, Yokogawa, and more.​

 

[Chan Tran]

Of course this raises the issue is whether the NEC puck used for calibrating monitors is calibrated. NEC recommends calibrating your monitor every month or so. But I don;t know if they have a way of verifying and calibrating the puck

Let try and see how close or how far apart your Minolta Autometer III F and the NEC Puck are.

 

[wiltw]

Anyone with a digital camera could expose a grey card per its meter, then check the resulting histogram to verify that the histogram peaks at exactly the center; or adjust the exposure until the histogram peaks in the center, then note the shutter speed + aperture combination that results in the centering of the peak...that can become the baseline exposure, and other meters with same combination are match to the histogram-matched exposure.

 

[BrianShaw]

I wonder who will be the first person to actually request a quote from ILT (or Spectra) and take the discussion beyond “I saw on the internet…”? My guess is that calibration service is very expensive, especially for the cheapskates who hang around this cozy pub.

 

[DREW WILEY]

Probably true, Brian, unless its one of their own cine meters under warranty. Calibrating film camera light meters is a very small niche even cumulatively, although still critical to a distinct segment of the well funded movie industry. There are far more industrial and scientific applications nowadays, where the very definition or a light meter is somewhat different from ours.

But if I wanted a second opinion about the calibration of my own meters, even though they all agree, I'd just reach for my Sekonic lux meter and do the conversion math. No need to second-guess histograms dependent on TTL and algorithm idiosyncrasies, or convoluted computer screen innovations, or even reach for my expensive darkroom projection densitometer, which is not only two decimal points more accurate than any light meter I've ever owned, but also over much wider luminance range. Or maybe I should talk to someone up at Lawrence Berkeley Lab, where they know how to measure a single photon, then add them all up.

 

[Sirius Glass]

If one has two or more meters and they disagree in their measurements on scenes and on gray cards, which meter should be chosen to be the standard for all of them? Why?

 

[BrianShaw]

If one has two or more meters and they disagree in their measurements on scenes and on gray cards, which meter should be chosen to be the standard for all of them? Why?

Oh… I know the answer. Trust the meter you sent out for calibration.

 

[DREW WILEY]

I dunno, Sirius. My meters all read exactly the same when brand new, and still do, given just two instances of formal recalibration over the past 45 years. When the very first one needed to be held together with electrical tape due to all those years of hard use, I decided to retire it, even though it still read correctly, and find another one. And I did indeed stumble onto a pre-owned but apparently never used Pentax digital spot meter for only $200. Before purchase, I checked it against one of my other ones, and it read identically over the full range.

I do have an ancient Weston light meter which I inherited from my brother, and keep in my fun useless stuff drawer. If there were still an owner's manual around, I suspect it would state, "Look left, then right, go to the chicken shed and pluck a feather to see which direction the wind takes it, then count till you can't see it anymore, multiply that by four and divide by six, and use that as your shutter speed. "

 

[Sirius Glass]

Oh… I know the answer. Trust the meter you sent out for calibration.

You broke the code!

 

[Sirius Glass]

I dunno, Sirius. My meters all read exactly the same when brand new, and still do, given just two instances of formal recalibration over the past 45 years. When the very first one needed to be held together with electrical tape due to all those years of hard use, I decided to retire it, even though it still read correctly, and find another one. And I did indeed stumble onto a pre-owned but apparently never used Pentax digital spot meter for only $200. Before purchase, I checked it against one of my other ones, and it read identically over the full range.

I do have an ancient Weston light meter which I inherited from my brother, and keep in my fun useless stuff drawer. If there were still an owner's manual around, I suspect it would state, "Look left, then right, go to the chicken shed and pluck a feather to see which direction the wind takes it, then count till you can't see it anymore, multiply that by four and divide by six, and use that as your shutter speed. "

Once I started shooting slides when I was 18 or 19, I sent any camera or light meter in for servicing or calibration, respectively.

 

[BrianShaw]

LOL, the Weston manuals aren’t quite that poetic. Weston meters are actually quite useful when they work. And when used as per the user manual. Often they are held/pointed wrong and that skews the reading. I have three and two work quite effectively; a Weston III and V. The third, another Weston III, reads 1 stop too high. So much for decline as the selenium cell ages…

 

[Chan Tran]

I have reply from ACS Calibration and they do not calibrate exposure meters.

 

[RalphLambrecht]

I don't see they mention exposure meter.

I think, I'm going to stick to the sun and'sunny-16', close enough for me.
best explained here:

 

[wiltw]

If one has two or more meters and they disagree in their measurements on scenes and on gray cards, which meter should be chosen to be the standard for all of them? Why?

The one that is not wrong, of course!

I just tried to write a note of inquiry to International Light Technologies on their web site, and one bit of information that they requested was (my words) 'in what category is your question', and since none of the selections were suited for photographic exposure meter check/adjust, I didn't bother to hit Send.

 

[Chan Tran]

I think, I'm going to stick to the sun and'sunny-16', close enough for me.
best explained here:

Both of his meters are wrong. The Sekonic read 2/3 stops too high and the Minolta 1/3 stop too high. According to the sunny 16 rule the meter should read at ISO 400 the shutter speed is 400 and aperture is f/16. But if he uses 1/500 shutter speed the aperture should be f/11 and 7/10 or f/11 and 2/3.

 

[Sirius Glass]

Both of his meters are wrong. The Sekonic read 2/3 stops too high and the Minolta 1/3 stop too high. According to the sunny 16 rule the meter should read at ISO 400 the shutter speed is 400 and aperture is f/16. But if he uses 1/500 shutter speed the aperture should be f/11 and 7/10 or f/11 and 2/3.

For a scientific wild ass guess [SWAG] one could start with Sunny 16 as a standard source.

 

[Chan Tran]

For a scientific wild ass guess [SWAG] one could start with Sunny 16 as a standard source.

What I don't like about what he did is that he used 1/500 because he considered it's close enough to 1/400 but the meter read 16 and 4/10 and he said it's 4/10 too high.

 

[Sirius Glass]

What I don't like about what he did is that he used 1/500 because he considered it's close enough to 1/400 but the meter read 16 and 4/10 and he said it's 4/10 too high.

Good point!

 

[wiltw]

I think, I'm going to stick to the sun and'sunny-16', close enough for me.
best explained here:

For a scientific wild ass guess [SWAG] one could start with Sunny 16 as a standard source.

But, to counterpoint that method...if I believed Sunny 16 to be a good rule of thumb, if I 'calibrated' my incident meter to f/16 within the past 2 weeks, it would be -0.2EV compared to pre-'calibration', and if I calibrated my incident meter to f/16 a few months ago, it would currently be -0.7EV compared to the same pre-'calibration' measurement. IOW the calibration brightness had CHANGED by 2/3EV just depending upon when I did that procedure shown in the video?! Yes, it is a WAG, but not close enough to be scientific.