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Kino Flo Colour Innaccuracy

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#1 JamesOldham

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Posted 23 July 2014 - 05:42 AM

Hi, this will be my first post to the forum.

 

When I hire in gear for TV commercial shoots, I will normally include 4-Bank kinos.

 

I've noticed that when 5500k tubes are in the colour looks great. Very accurate it seems and compliments light from HMIs (with maybe 1/8 CTO) very well

 

However, when it comes to changing colour temps for different moods, and I switch to the tungsten tubes, they are never quite as pleasing.

There's almost a muddy pink/magenta shift in the colour of the light. I often end up just throwing CTO over instead now as it's much quicker anyway.

 

I don't believe this is anything to do with the rental company holding faulty tubes as I've experienced this elsewhere too.

 

Has anyone ever noticed this before?

 

James Oldham

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#2 Phil Rhodes

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Posted 23 July 2014 - 05:52 AM

I've not noticed that - so far Kino tungsten seems to be the only fluorescent tungsten worth using. Almost creamy in appearance. Unfortunately I can't really offer more than that subjective impression, but - no, not something I've noticed. I guess you could get the feeling they were muddy because they're warmer, but other than that I can't account for it.

 

Tungsten is technically "harder" to achieve with flos; the blue phosphors are - I assume - wider-bandwidth, which is why cooler flos tend to have better CRI. But that's something that's clearly been worked on a lot.

 

I'm not sure CTO will work terribly accurately on daylight flos.

 

P


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#3 Chad Griepentrog

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Posted 23 July 2014 - 10:13 AM

I run into more issues with Kino's Diva series lights. 1/8th or 1/4 plus green is always on hand for these.
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#4 Adrian Sierkowski

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Posted 23 July 2014 - 11:16 AM

You're hitting into, as Phil mentions, the fact that for your plasma based lights-- or better put phosphor based, such as Kino, LEDs etc, they ten towards blue and are pretty deficient in the red end of the spectrum. As such, even when you get them, roughly, 3200K, they're missing some wavelengths which you'd get with a comparable tungsten head-- and as such a little bit of the "life" of the colors in front of you. This is much exacerbated by anything else tungsten in the screen which gives you a "baseline" reference-- at least to my eye this seems to be the case, though I haven't really metered them. It's also a reason I tend to not use Kinos unless i have to-- and even then primarily daylight.

Something you can do to help, is to "trick" your eye a bit-- reglobing the practicals in the scene with photoflood bulbs so they go a little cooler, and perhaps using some 1/8 CTB on any tungsten heads you're using in your lighting. This will help, I find, to make the kinos as a key, pop a bit more.


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#5 Satsuki Murashige

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Posted 23 July 2014 - 11:44 PM

Are you having problems with the 3200K tubes? Kino also make 2900K tubes that a lot of people prefer when mixing with tungsten sources. Might be worth trying.
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#6 James Oldham

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Posted 24 July 2014 - 01:57 AM

Thanks for the suggestions.

I am using the 3200k tubes.

I actually wasn't aware that 2900k tubes were available. I will have to look into this as it sounds to be an interesting prospect.

 

It is not often that I will use the 3200k tubes on the 4 bank, but when I do, I've always felt it to be lacking in some wavelengths of the colour spectrum.

It would be interesting to see a spectral chart on the fixture.

 

In fact, i just did a quick search on kino website with regards to this: http://www.kinoflo.c...True_Match.html

 

I don't notice anything on the chart that would suggest towards a magenta/pink shift in the 3200k. Although the 2900k tube looks interesting, with a slight spike just below 600nm (which is maybe why it looks more pleasing Satsuki?)

 

Adrian, I think your technique makes sense, and I should try this sometime on a future project.


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#7 Phil Rhodes

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Posted 24 July 2014 - 02:18 AM

I've always felt it to be lacking in some wavelengths of the colour spectrum.

 

Like all fluorescent tubes - they are. It's just designed not to be objectionable.

 

The only other thing I can think of is that ballasts which under-run fluorescent tubes may cause them to drift toward the magenta, or over-driven tubes may go yellowish. 

 

P


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#8 Stuart Allman

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Posted 24 July 2014 - 10:07 AM

A while back I measured the Diva K55 and K32 tubes using the MK350 spectrometer.  I thought you might be interested in the results.

 

http://videogearsand...ly-perform.html

 

The pictures show the CCT, CRI and CIE 1931 coordinates.  In this case the K32 bulbs were a bit closer to target than the K55 bulbs in terms of CCT an CRI - but that's not the complete story. 

 

In theory a D55 (5503K) illuminant should have a CIE 1931 coordinate of (x,y)=(0.332,0.347).  The K55 bulb showed a reading of (x,y)=(0.308,0.315), which is much more blue.  The bulb is performing much closer to a F1 (fluorescent daylight) standard illuminant.

 

Since I don't have a good reference for the color coordinates for 3200K, nor time to calculate it, I'll reference a 3000K illuminant.  This is pretty close to the CCT the MK350 spectrometer said the K32 bulb is anyway.  That should have a CIE 1931 coordinate of about (x,y)=(0.25, 0.35), whereas the bulb measures (0.422,0.382) which is WAY more green.  It's much closer to an F12 (3000K fluorescent) standard illuminant.

 

If you look up "CIE 1931" and "D55 standard illuminant" on Google the Wikipedia pages are actually quite good.  The half-ellipsoidal chart should immediately pop up when you type in "CIE 1931".  That will show you how (x,y) coordinates correlate to colors.

 

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#9 Stuart Allman

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Posted 24 July 2014 - 10:34 AM

Sorry, my stupid mistake...I was looking at my (u,v) data instead of (x,y).  Stack it up to an early morning.

 

Edit the above...

 

A 3100K source should have a CIE1931 color coordinate of (0.419,0.401), NOT what I stated above.  So a K32 bulb with a measurement of (0.422,0.382) is a bit more orange-ish/red.


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#10 Satsuki Murashige

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Posted 24 July 2014 - 10:43 AM

I think the 2900K tubes are meant to match actual tungsten sources which often run slightly warmer than the nominal 3200K. So for mixed source environments they work better.
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#11 Stuart Allman

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Posted 24 July 2014 - 11:50 AM

On the way to work today, I was thinking about the K55 Kiva tube measurement being 6942K. If we consider the nearest camera setting of 6900K, that's a CIE 1931 of (x,y)=(0.308,0.318).  In that case the K55 tube seems to rate really well as a 6900K source.  I wonder where Kino-Flo got their K55 (seeming to allude to 5500K) name from?  It would be interesting to hear their comments if they have a representative on this forum.


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#12 James Oldham

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Posted 24 July 2014 - 11:57 AM

Thanks for all that juicy information Stuart.

 

I've always thought that the Kinos complimented Arri's HMI line rather nicely.

 

It would be interesting to hear from Kino on the thread...


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#13 David Landau

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Posted 28 July 2014 - 09:04 PM

I have never had an issue with the 4 bank 4 ft kinos. I have had issues with the Diva's turning magenta. As others have stated, there are certain wavelengths missing from any phosphor light source. The questions becomes, how offensive is it? In the real world we see a wide variety of light sources in all colors, textures in a variety of intensities coming from all directions. When lighting, we concern ourselves with supporting the material being shot with the visuals. So, the question shouldn't be as much is the source a true 3200k but rather does the source work for the intent of the scene being shot. Does it support the emotional moment that the piece is trying to convey to the viewer? if the source is producing a magenta light that pulls the viewer out of the moment or doesn't work for the desired look, then it should be gelled or otherwise corrected.

 

Many famous cinematographers have been commenting lately that they fear so many new camera people have forgot how to light - how to use their eyes to light something that supports the story. Some blame this on the massive attention to new technology and being absolutely exact while others blame this on the high sensitivity cameras that can get an acceptable image with no lighting. While we need to have reliable units and we have to pay attention to their kelvin degrees, the end judge should be the human eye and the feeling the image generates.


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#14 Guy Holt

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Posted 29 July 2014 - 06:53 AM

Many famous cinematographers have been commenting lately that they fear so many new camera people have forgot how to light - how to use their eyes to light something that supports the story. Some blame .... blame this on the high sensitivity cameras that can get an acceptable image with no lighting.

 

I agree 100%. That you can get a serviceable image with an Alexa with available light doesn’t mean that you don’t need to light a shot. The problem with working with available light is that it is not always what you want for a scene. This trend towards making pictures “without too much help from the electric department” is IMO troubling because the DOP is giving up authorship of the image. If his/her options are limited to what the great Gaffer in the sky happens to provide that day, the creative options are limited.  And if by chance the available light does happen to coincide with what is creatively desired, it will invariably change in the course of the production, leaving the editor with a continuity nightmare.  IMO, it is better to tame the natural daylight, and use lights to create a consistent and aesthetically appropriate look that models your set and talent as you wish, than to limit yourself to what your dealt that day and take your chances.

 

Guy Holt, Gaffer, SceenLight & Grip, Lighting and Grip Rental in Boston.


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