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Sekonic C-500 Color Meter and CC value interpretations

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#1 Chad Terpstra

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Posted 20 November 2013 - 11:48 PM

I just recently purchased a Sekonic C-500 color meter in order to know how much CTO, CTB or +/- Green to add to lights to match different environments. I'm wondering how to directly interpret the readings of the meter into the most common denotation of gel strengths - i.e.   1/8,1/4, 1/2 and Full (Color). I can figure out Kelvin with some quick math but where do you find what strength of +/- green to use? The meter reads 0-50 Magenta and 0-50 Green. 

 

Also the readings in digital mode are very different than in film mode. For example a reading in digital mode of CC filter 5M will be CC filter 25M in film mode. Anyone using this meter that could lend me some incite? 


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#2 Guy Holt

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Posted 21 November 2013 - 06:12 AM

I just recently purchased a Sekonic C-500 color meter in order to know how much CTO, CTB or +/- Green to add to lights to match different environments. 

 

What types of lights do you plan to correct with this meter?

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Eq. Rental & Sales in Boston


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#3 Chad Terpstra

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Posted 23 November 2013 - 01:36 AM

 

What types of lights do you plan to correct with this meter?

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Eq. Rental & Sales in Boston

 

 

All types of light ideally. Tungsten, HMI, Fluorescent LED, etc. I've heard some meters aren't compatible with LED but I don't know about this one. 


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#4 Guy Holt

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Posted 23 November 2013 - 07:12 PM

....where do you find what strength of +/- green to use? The meter reads 0-50 Magenta and 0-50 Green. 

 

Also the readings in digital mode are very different than in film mode. For example a reading in digital mode of CC filter 5M will be CC filter 25M in film mode. Anyone using this meter that could lend me some incite? 

 

Use this link for a table that correlates CC (Color Compensating) values and Color Correction Gel (plus and minus greens.) The reason for the discrepancy is that different imaging tools will see a discontinuous  spectrum in different ways. Film is much more sensitive to blue and green, which is why fluorescent lights will photograph with a severe green/cyan cast. The same lights seen through an HD or video camera may appear fairly neutral. They may look a touch green, but nothing that can’t be easily corrected. A typical three-chip camera doesn’t have the same wide gamut that a film stock does, so it won’t see certain colors as strongly. In such a case, color correction that works for film may be overkill for a digital imager. Fortunately, when shooting digitally, we can see what we’re doing.

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting rental and sales in Boston


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#5 Chad Terpstra

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Posted 04 December 2013 - 08:11 PM

 

Use this link for a table that correlates CC (Color Compensating) values and Color Correction Gel (plus and minus greens.) The reason for the discrepancy is that different imaging tools will see a discontinuous  spectrum in different ways. Film is much more sensitive to blue and green, which is why fluorescent lights will photograph with a severe green/cyan cast. The same lights seen through an HD or video camera may appear fairly neutral. They may look a touch green, but nothing that can’t be easily corrected. A typical three-chip camera doesn’t have the same wide gamut that a film stock does, so it won’t see certain colors as strongly. In such a case, color correction that works for film may be overkill for a digital imager. Fortunately, when shooting digitally, we can see what we’re doing.

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting rental and sales in Boston

 

 

 

Thanks for the reply, Guy. That makes sense and the link has a lot of great info for what to expect with a color meter. I've done a bit more testing and the digital setting seems to be tracking really well with my 5D's white balance settings when viewing a white card on a vectorcsope. 

 

As far as the +/- green gel I think the best thing to do is just meter different strengths of gel and make your own table you know and trust with your meter. That's the best way to be sure. 

 

It's too bad about LED sources not being accurate. According to Konica/Minolta their CL-200A meter can read LED. Once you find out the price though you'll second guess the worth of it though - $3,400! http://sensing.konic...a-chroma-meter/  

 

The only thing left that has me puzzled still is that I often get a reading that says "Under" which I've figured out means it's too warm or under the sensor's Kelvin range to accurately measure. This is odd though because it seems to happen to incandescent bulbs that are even slightly dimmed (i.e. a bulb starts at around 2800K and as soon as you dim it the meter can't read it). This is in either range setting -high or low. I'm going to call Sekonic and confirm this is normal because it seems like it should be able to read a little lower than that. My friend's 20 year-old Minolta meter was reading them with no problem. 


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#6 Guy Holt

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Posted 04 December 2013 - 10:14 PM

 According to Konica/Minolta their CL-200A meter can read LED. Once you find out the price though you'll second guess the worth of it though - $3,400! http://sensing.konic...a-chroma-meter/

 

According to Konica Minolta’s website, the 200A is not intended for measurement for photographic corrective purposes but rather for LED billboard quality control and maintenance. If LED modules that are side by side on LED billboards have different color tones (because of lumen depreciation and color shift), the billboard will look mottled. By providing a means of measuring the chromaticity and color of LED modules using Δuv readings, the CL-200A enables billboard developers and maintenance personnel to assure billboard uniformity and clarity of color. To be useful in photography, a color meter must measure the color of light and present the data in terms that a photographer can use. Unfortunately, the Δuv readings that the 200A provides do not translate to CC (green/magenta) or LB (CTB/CTO) gels. For this reason the 200A cannot be used for photographic corrective measurements.

 

Unfortunately there is no color meter that provides a valid means of color correcting LED luminaries for photographic purposes. The CC (Color Compensating) and LB (Light Balancing) scales used by color meters are not calibrated for the discontinuous spectral output of LEDs, but only continuous spectrum sources like tungsten, HMI, & Fluorescent. The typical color meter has three sensors that measure specific wavelengths of red, green or blue. The assumption is that all three of these wavelengths will occur naturally in a black body radiator, which is a theoretical source that radiates light across all wavelengths and changes color temperature as it is heated. When we talk of a 3200k or 5600k light source, what we’re referring to is the color of light emitted by a black body radiator that is heated to 3200k or 5600k. It’s true that 3200k light is warmer than 5600k light, but that doesn’t mean that the black body source has stopped radiating at certain wavelengths. What has changed is that some wavelengths are being radiated more than others—in the case of 5600k light, more blue is being emitted than red, but red is never completely eliminated. The problem with the discontinuous spectrum of LED sources is that certain wavelengths are deficient or absent all together (use this link for details.) Using a color meter with these sources can result in faulty correction, as colors are typically presented as ratios (orange to blue, green to magenta) and only one half of the equation may not be present.

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting rental and sales in Boston


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