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Author Topic: NEC Spectraview II and Light Meter calibration  (Read 2376 times)

Alan Klein

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NEC Spectraview II and Light Meter calibration
« on: January 29, 2018, 04:45:18 PM »

I have a NEC PA242W monitor with Spectraview II calibration kit.  I also have a hand held meter (Minolta IIIf for incident and reflective measurements).  Is there a way to use the NEC equipment to check and calibrate the meter?

aaron125

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Re: NEC Spectraview II and Light Meter calibration
« Reply #1 on: January 29, 2018, 04:58:35 PM »

Not in any way I can think of. The Spectraview II kit, if I'm not mistaken consists of a re-badged X-Rite i1 display pro colorimeter and there's no possible way that a colorimeter can conceivably calibrate or even have any kind of interaction with a incident/reflective light meter.

Perhaps someone wiser than I could recommend some manner in which they could instruct you to somehow measure a specific light source (it would have to be an extremely stable light source, and would likewise require an incredibly stable power supply to run said light source as a standard 110/220V wall socket is anything but stable, nor are they likely to be within 1-5% of their nominal voltages). Considering that your light meter probably measured down to either 1/3 stop or even perhaps 1/10 stop, this is quite a task indeed.

Lastly, you'd only be able to calibrate at best, if even possible at all, the incident measurements of your light meter. There's no way you'd be able to do anything at all with regard to reflective measurements on your light meter.

If anyone has any ideas or can tell me where I've mentioned something incorrect or I've mistaken something, please correct me - I'm here to, and happy to, learn as much as possible.


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Alan Klein

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Re: NEC Spectraview II and Light Meter calibration
« Reply #2 on: January 29, 2018, 05:08:35 PM »

Thanks Aaron for your thoughts.  Beside color, the "puck" also measures light intensity in cd/m squared.  The light meter can read and calibrate the monitor's display to a specific setting.  Could you use the meter to look at the monitor's display?

Additionally, the ambient reading of the NEC puck reads ambient light which would be an incident light reading of outdoor or indoor lighting.  Could this also be used to calibrate the meter?

DP

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Re: NEC Spectraview II and Light Meter calibration
« Reply #3 on: January 29, 2018, 05:09:14 PM »

I have a NEC PA242W monitor with Spectraview II calibration kit.  I also have a hand held meter (Minolta IIIf for incident and reflective measurements).  Is there a way to use the NEC equipment to check and calibrate the meter?

you mean you want to set a monitor to a specific brightness with SpectraView II and then use it to see how minolta is metering ?
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Alan Klein

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Re: NEC Spectraview II and Light Meter calibration
« Reply #4 on: January 29, 2018, 05:19:47 PM »

Here's what I just tried.  With the NEC monitor calibrated for 140cd/m2 I placed the reflective meters (both a Minolta IIIf and Sekonic L-158) against the white portion of the monitor's screen and got an EV of 10.5.  That's interesting.  Is that what they should read?  Accurate? 

Alan Klein

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Re: NEC Spectraview II and Light Meter calibration
« Reply #5 on: January 29, 2018, 05:20:52 PM »

you mean you want to set a monitor to a specific brightness with SpectraView II and then use it to see how minolta is metering ?
Yes

Alan Klein

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Re: NEC Spectraview II and Light Meter calibration
« Reply #6 on: January 29, 2018, 05:24:37 PM »

Actually the Minolta read 10.6 and the Sekonic looks like 10.4.  That's really close.  I'd try my P&S but I don;t think it has EV readings.   Is EV what I should read with the NEC monitor calibrated for 140cd/m2? 

DP

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Alan Klein

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Re: NEC Spectraview II and Light Meter calibration
« Reply #8 on: January 29, 2018, 09:24:42 PM »

Thanks DP.  That gave me an idea on how to try my digital camera.  So I set its ISO on 100, aperture priority on f8 and aimed the view at just the white on the monitor a couple of inches away.  1/20 of a second was the speed the camera selected.  If you go to the EV tables, that's the equivalent of an EV of 10.5, the same as both of the hand held light meters.   So both meters and the camera indicates an EV of 10.5 from the screen calibrated at a light intensity of 140cd/m2.  It would seem that all three are in calibration.  Discussion? Is this a quirk?

Does anyone know if there is a formula to convert a monitor's light intensity setting to an EV so you can calibrate any reflective light meter, hand held or internal to a camera? 

Czornyj

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Re: NEC Spectraview II and Light Meter calibration
« Reply #9 on: January 30, 2018, 03:52:16 AM »

What you’re planning to do is really, really the worst idea you can think of. There’s no chance that light meter can make an accurate measurement of monitor brightness - and it apparently doesn’t - 140cd/m^2 is 10.13EV, so as you can see there’s ~0.5EV error in lightmeter reading, as expected.

You can measure daylight using i1D3, but it’s also uncertain if such measurement will be accurate. Lightmeter was built to measure daylight, i1D3 was built to measure monitor backlight, two completly different animals.
« Last Edit: January 30, 2018, 05:11:39 AM by Czornyj »
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GWGill

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Re: NEC Spectraview II and Light Meter calibration
« Reply #10 on: January 30, 2018, 06:06:27 AM »

Lightmeter was built to measure daylight, i1D3 was built to measure monitor backlight, two completly different animals.
Actually, the i1d3 is more likely to be accurate measuring daylight than a typical light meter. The i1d3 has filters that are manufactured to be reasonably close to the standard observer spectral response. I'm not sure any light meter has filters of comparable accuracy, short of something approaching laboratory grade.
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Czornyj

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Re: NEC Spectraview II and Light Meter calibration
« Reply #11 on: January 30, 2018, 08:02:55 AM »

Actually, the i1d3 is more likely to be accurate measuring daylight than a typical light meter. The i1d3 has filters that are manufactured to be reasonably close to the standard observer spectral response. I'm not sure any light meter has filters of comparable accuracy, short of something approaching laboratory grade.

Graeme, you're 100% right  (as usual) - assuming it is very close to standard observer CMF it should measure daylight with accuracy higher than a typical light meter, so it could be considered as a reference measurement source for light meter calibration.

DP

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Re: NEC Spectraview II and Light Meter calibration
« Reply #12 on: January 30, 2018, 08:24:04 AM »

What you’re planning to do is really, really the worst idea you can think of. There’s no chance that light meter can make an accurate measurement of monitor brightness

what he does (apparently) is trying it establish how his light meters are calibrated vs camera metering... so he really does not need to set a light/illumination source to any specific cd/m^2 - he just needs to make sure that he is using light meter and camera against that source (with some stable output whatever it is) in a consistent manner to compare their readings ... $0.02
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Czornyj

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Re: NEC Spectraview II and Light Meter calibration
« Reply #13 on: January 30, 2018, 08:30:14 AM »

what he does (apparently) is trying it establish how his light meters are calibrated vs camera metering... so he really does not need to set a light/illumination source to any specific cd/m^2 - he just needs to make sure that he is using light meter and camera against that source (with some stable output whatever it is) in a consistent manner to compare their readings ... $0.02

Using a GBr LED backlit display a light source for such evaluation is a bad idea. Light meters will be fooled by spiky SPD of such light source.

Alan Goldhammer

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Re: NEC Spectraview II and Light Meter calibration
« Reply #14 on: January 30, 2018, 08:52:42 AM »

I am not familiar with the Minolta meter and wonder if there is a way for a user to calibrate it against a known light source.  I know that my antique Sekonic L-228 cannot be manually calibrated.  The only user control is the zero light adjustment.  Back in the day when I compared my Nikon F internal metering system against the Sekonic I simply used a Kodak gray card in a shady area so the illumination was uniform and compared the two meter readings.  They were close to identical.
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DP

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Re: NEC Spectraview II and Light Meter calibration
« Reply #15 on: January 30, 2018, 09:01:30 AM »

Using a GBr LED backlit display a light source for such evaluation is a bad idea. Light meters will be fooled by spiky SPD of such light source.

but his test shows that both low grade light meters in fact are as fooled as his camera and they all meter quite similar for most practical purposes- that was the whole point ... we are not talking about lab grade precision here
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Alan Klein

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Re: NEC Spectraview II and Light Meter calibration
« Reply #16 on: January 30, 2018, 11:13:03 AM »

Thanks all.  First, I don;t  know what the light output of the monitor is.  The 140cd/m2 is the max.  Where do you find the actual measured by the puck in the Spectraview II program?  Even if it's equal to 10.13, that's pretty close to the three readings of 10.4, 10,5 and 10.6 I got.  I'm sure the Spectraview itself has a percent of inaccuracies.

But the main point is that all three are close.  That really surprised me considering the ages of the two meters are over 35 years.  Of course I could aim at an overcast sky to see how they match.  Has anyone tried that?

My main interest is to make sure I'm getting proper readings on my Minolta light meter which has an adjustment screw.  That's what I use when I shoot negative and positive film.  Is using a digital camera to adjust the Minolta meter a reasonable approach?  Any recommendations on how to go about this?

digitaldog

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Re: NEC Spectraview II and Light Meter calibration
« Reply #17 on: January 30, 2018, 12:27:56 PM »

Where do you find the actual measured by the puck in the Spectraview II program?
Report window just after it finishes. And I agree with others, this is a rabbit hole you don't want to jump into (with respect to the Minolta).

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Andrew Rodney
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Alan Klein

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Re: NEC Spectraview II and Light Meter calibration
« Reply #18 on: January 30, 2018, 01:55:00 PM »

No rabbit holes for me.  :)

 My concern is that the Minolta is in calibration and appears to be as it matches the digital camera and other meter which could both be used as backups.

Alan Goldhammer

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Re: NEC Spectraview II and Light Meter calibration
« Reply #19 on: January 30, 2018, 02:06:44 PM »

My main interest is to make sure I'm getting proper readings on my Minolta light meter which has an adjustment screw.  That's what I use when I shoot negative and positive film.  Is using a digital camera to adjust the Minolta meter a reasonable approach?  Any recommendations on how to go about this?
Here is how I would do it.  Get an 18% gray card and take the meter reading using your Minolta.  Set your DSLR manually to capture that image.  then take a couple of images on either side of the meter reading. Take it into Photoshop and see which of the images is most accurate to what the real values should be.  See:  https://en.wikipedia.org/wiki/Middle_gray  for the rgb and LAB values.  You should know if your meter is accurate and if not, which direction it deviates.  I don't know how fine the adjustment screw is but you will probably have to repeat the test to make sure the adjustment gives you the correct value.

The easier approach is to see if there are any repair people out there that do calibration work on light meters.  One other problem that you might have is that some of the older light meters were designed to run on the older mercury batteries that are not manufactured any longer.  You may not be able to find a newer battery that is an exact replacement and you either need to make an adapter or have one made so that your light meter works correctly:  https://www.nadir.it/pandora/PILE-PX625.pdf


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