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Minolta Color Meter II


Bryce Lansing
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My Dad let me borrow his Minolta Color Meter II, and I have been using it for the past year. He's had it for a while, but it has always been taken care of and well stored.

 

I was always taught that the color temperature of a tungsten bulb is 3200K. But for as long as I've been using this color meter, whenever I take a reading off a tungsten light, it says 2800K. Whether its a Lowell tota, omni, Mole tweenie, baby, etc., even tungsten Kinoflo bulbs, they all read 2800K, sometimes even 2700. I took a reading off a 60w household incandescent bulb, and it said 2400.

 

Is there something wrong with my meter? Does it need to be re-calibrated? Or are these readings right?

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My Dad let me borrow his Minolta Color Meter II, and I have been using it for the past year. He's had it for a while, but it has always been taken care of and well stored.

 

I was always taught that the color temperature of a tungsten bulb is 3200K. But for as long as I've been using this color meter, whenever I take a reading off a tungsten light, it says 2800K. Whether its a Lowell tota, omni, Mole tweenie, baby, etc., even tungsten Kinoflo bulbs, they all read 2800K, sometimes even 2700. I took a reading off a 60w household incandescent bulb, and it said 2400.

 

Is there something wrong with my meter? Does it need to be re-calibrated? Or are these readings right?

 

Household bulbs generally are below 3200K, more like 2800K. Kino tubes come in 2900K and 3200K varieties. Older globes like in a tweenie can start to go below 3200K. Also, the power supply can affect a tungsten lamp, perhaps something was causing them to be under-powered.

 

All that said, I don't know if the meter needs recalibrating or not.

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On a bright sunny day I usually get a reading anywhere from 4800K-6000K. Now that I think of it too, when I took a reading of KinoFlo Daylight tubes, it read 4800K. Then I shot the camera at 5600k, and the skin tone looked normal, not noticeably warmer. -800k would be noticeably warmer right?

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My Color Meter II was off quite a bit when I bought it. I sent it to Quality Light Metric for calibration and when I got it back it read 3200K Halogen fixtures (running at close to the bulb voltage ratings of 120V) and GE Chroma 50's in fixtures with magnetic ballasts right on the money.

 

QLM (323) 467-2265. They're located in Hollywood, the drop off address is on the NE corner of Hollywood & LaBrea. They do pick ups twice a day. Average meter repair is between $55 & $85 with a 1-2 day turnaround.

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My Color Meter II was off quite a bit when I bought it. I sent it to Quality Light Metric for calibration and when I got it back it read 3200K Halogen fixtures (running at close to the bulb voltage ratings of 120V) and GE Chroma 50's in fixtures with magnetic ballasts right on the money.

 

QLM (323) 467-2265. They're located in Hollywood, the drop off address is on the NE corner of Hollywood & LaBrea. They do pick ups twice a day. Average meter repair is between $55 & $85 with a 1-2 day turnaround.

 

Thanks! I started getting worried.. I've been looking for a place to re-calibrate for the past few days, and it was looking like not even Minolta themselves repaired/calibrated that model anymore.

 

I will definitely check out QLM

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  • 8 years later...

Hello!

The info about QLM is still very helpful 8 years later, many thanks!

 

I have one additional question. I picked up a Minolta Color Meter II on eBay. Knew the risks, and low and behold it's wayyyy off. metering 4k on a cloudy day.

 

Does anyone know if the calibration happens in the head or in the meter itself? There are a few new heads available online. However, these heads are all labeled "Flash Color Receptor" as opposed to "Minolta Color Meter II" (which is how mine is labeled)

 

Does anyone have experience swapping out the head?

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  • 3 years later...
On 7/1/2017 at 12:45 PM, Gabriel Elder said:

I picked up a Minolta Color Meter II on eBay. Knew the risks, and low and behold it's wayyyy off. metering 4k on a cloudy day.

Hey Gabriel, did you get your meter calibrated? I just got a Minolta Color Meter II and the readings are not even close to what I should expect. Actually as you mentioned all the measurements that I took came low.

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I have one similar meter which needs calibrating too.  I took the sensor apart a while ago to see how complicated it would be to calibrate but there is lots of trimmers affecting the calibration so it would be at least good if someone could advice which trimmer affects which adjustment 

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2 hours ago, aapo lettinen said:

I have one similar meter which needs calibrating too.  I took the sensor apart a while ago to see how complicated it would be to calibrate but there is lots of trimmers affecting the calibration so it would be at least good if someone could advice which trimmer affects which adjustment 

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  • 1 month later...
On 5/8/2021 at 4:58 AM, Ruben Arce said:

Hey Gabriel, did you get your meter calibrated? I just got a Minolta Color Meter II and the readings are not even close to what I should expect. Actually as you mentioned all the measurements that I took came low.

I never did unfortunately, but seeing your post has given me renewed interest.  I may give Quality Light Metric (mentioned above in this thread) a call, assuming they're still operating!

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Aapo, it's amazing to see those PCBs!  That is certainly an intimidating number of pots.  I did some superficial searches for a schematic to no avail.  The tricky thing, at least in my case, is that the meter is inaccurate, and inconsistent.  When I originally bought it I tried compensating for the error using a SkyPanel as a ref point but it was impossible to find a consistent error in the readings.

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QLM is out of business. I called the number and spoke with the friendly business owner. He referred me to SPECTRA Cine Meters 818.954.9222 . He said they might be able to service Minolta color meters.

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Yes, QLM is out of business and the man referred me to Spectra as well, so I sent my light meter and my Minolta Color Meter II and they deemed the Minolta unrepairable. They said the cells were not in good condition and they don't have parts. The one that I have was in great looking condition, but it was around 40 years old... So, I guess I'll better get a modern one.

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10 hours ago, Gabriel Elder said:

Aapo, it's amazing to see those PCBs!  That is certainly an intimidating number of pots.  I did some superficial searches for a schematic to no avail.  The tricky thing, at least in my case, is that the meter is inaccurate, and inconsistent.  When I originally bought it I tried compensating for the error using a SkyPanel as a ref point but it was impossible to find a consistent error in the readings.

the schematics can be worked out using the circuit board and datasheets of the components. probably I would want to open the actual meter too to see what is inside. But frankly speaking, that is so time consuming that I could probably make my own colour meter from scratch in the same time. I would probably use a attiny84 or atmega 328p microcontroller depending on the user interface needed. it would have a small oled display and it would be about 1/5th of the size of the Colour Meter II but a bit more  accurate and had more functions

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It's quite possible to build a very capable colour meter in a home workshop. Calibrating it, on the other hand...

Possibly the simplest (if least-portable) approach is a photomultiplier reading a monochromator. That sounds complicated, but what it really means is that you get a diffraction grating, mount it on a very accurate servoactuated rotating mount, and collimate the test light source through it onto the photomultiplier (which you can get as a finished module with all the driver electronics). That will happily give you a way to read a very accurate series of samples which will work at very low illumination levels.

Calibrating the wavelength is reasonably easy using commonly-available, very frequency-stable sources, such as sodium vapour lighting, a helium-neon laser, and more or less any mercury-based discharge lamp.

Calibrating the intensity, though, can really only be done using a precision reference light source that you'll pretty much just have to buy.

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10 hours ago, Phil Rhodes said:

It's quite possible to build a very capable colour meter in a home workshop. Calibrating it, on the other hand...

Possibly the simplest (if least-portable) approach is a photomultiplier reading a monochromator. That sounds complicated, but what it really means is that you get a diffraction grating, mount it on a very accurate servoactuated rotating mount, and collimate the test light source through it onto the photomultiplier (which you can get as a finished module with all the driver electronics). That will happily give you a way to read a very accurate series of samples which will work at very low illumination levels.

Calibrating the wavelength is reasonably easy using commonly-available, very frequency-stable sources, such as sodium vapour lighting, a helium-neon laser, and more or less any mercury-based discharge lamp.

Calibrating the intensity, though, can really only be done using a precision reference light source that you'll pretty much just have to buy.

practically one would just need to compare it to other meters to narrow down the calibration until it is good enough to be used for work. I would measure different sunlight situations and tungsten lights for starters and then move to discharge and led sources. I was thinking a simple sensor with 3 photocells or photodiodes and rgb filtering over them, then either a preamp or directly to a microcontroller and all the calibration done in software

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48 minutes ago, aapo lettinen said:

a simple sensor with 3 photocells or photodiodes and rgb filtering over them

There's a question over how useful such a meter (including the Minolta) would be with modern, particularly LED light sources. Done well, it could measure correlated colour temperature, magenta-green shift and potentially CIE xy coordinates, but only on the assumption that the light it's observing is a reasonable-quality white to begin with. It could not produce a spectrum or calculate indices such as CRI or TLCI. Handheld meters which do this, and simpler, cheaper monitor probes, tend to have at least several more colour filters and photosensors, and the best (non-photomultiplier) types may have linear CCDs and diffraction gratings. Even then, monitor probes that work like this need to be told what sort of backlight they're working with so as to make sensible assumptions about the characteristics of the light, and handheld colour meters tend not to work very well on highly saturated colours. I've measured direct-emission (that is, not phosphor-converted) LEDs and they read as sort of pseudo-gaussian curves, and I know for a fact that they should look a lot narrower than that on a spectrum chart.

So yes, if you just want a CCT and magenta-green shift meter, you could potentially do what you describe, but it can't give you the features of a UPRTek CV600 or Sekonic C800.

 

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one could make a linear ccd one in reasonable time if it only takes single measurements so that the readout from the sensor can be low with low sensor clock speeds. then the stream could be read directly by the microcontroller. If it needs to read at high speed (like for imaging applications) then it will become challenging. but no one needs such readout speed for a color meter anyway.

if making a meter it should be either very simple and small and efficient to make sense, or alternatively one could make one as a passion project and just not care how much time and resources it takes to build one.  Personally I would rather take the small and simple one because I am only needing this type of meters for colour temperature and green-magenta shift measurements.

if it would need to measure highly saturated LED light hue values accurately, then it would need to be more complicated. But one can manage without such meter in most shooting situations by just planning more carefully and using apps if needed.

Like always, one needs to evaluate what one really needs and which specs would be nice extra to have but more rarely needed. Making the simplified systems is easy but if one wants to include all and every possible features in a single device, then there is no other possibility than to make it as a passion project and spend even years of your life to the project. To me, that kind of dedication makes no sense at all. I would rather spend the time making something useful like actually shooting something than to waste time building something which is not needed 🙂

Edited by aapo lettinen
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