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how to get the correct color from hmi


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#1 thiyagucam

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Posted 05 August 2006 - 06:31 AM

if suppose i have to liht up one day effect sequence i am using par lights and hmi lights combinely but i felt little bit green or megenta has been came from the hmi how could i plan for correct color reproduction?
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#2 Stephen Murphy

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Posted 05 August 2006 - 08:02 AM

Are you using HMI Pars or Par Cans?
If you are trying to balance a HMI to a ParCan (Tungsten) then you need to put Full CTO in front of the HMI. You will loose 2/3rds of a stop of light by doing this.
If you are worried about your hmi being off color then first try replacing the bulb with a fresh bulb. Wait untill the light has come up to temperature and then measure it with a colour temp meter. Add Plus or Minus green if required. HMI's with older bulbs can turn a bit greenish and they do need to be checked regularly. Hope this helps,
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#3 kpv rajkumar

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Posted 05 August 2006 - 08:49 AM

Are you using HMI Pars or Par Cans?
If you are trying to balance a HMI to a ParCan (Tungsten) then you need to put Full CTO in front of the HMI. You will loose 2/3rds of a stop of light by doing this.
If you are worried about your hmi being off color then first try replacing the bulb with a fresh bulb. Wait untill the light has come up to temperature and then measure it with a colour temp meter. Add Plus or Minus green if required. HMI's with older bulbs can turn a bit greenish and they do need to be checked regularly. Hope this helps,


hi steve! let me tailgate this beautiful thermal!
is it ok if i gel the truant HMI's with 85 instead of Full CTO?
if so, then what are the trade offs in terms of stop loss?
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#4 Brian Drysdale

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Posted 05 August 2006 - 10:00 AM

Lee have a filter for converting HMIs to tungsten: http://www.leefilter....asp?PageID=298

Interestingly, the Full CTO is actually an over correction, the 3/4 CTO is the 5600K to 3200K conversion. Most people just throw on the Full CTO - generally I use it mostly for a sunset effect with the HMI, rather than using the HMI with tungsten light, so I'm not that worried about being accurate.

Someone pointed it out the other day - just shows you should keep reminding yourself about these things.

All very confusing compared to the CTBs.

Edited by Brian Drysdale, 05 August 2006 - 10:02 AM.

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#5 Stephen Murphy

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Posted 05 August 2006 - 10:48 AM

Actually id have to disagree with you there Brian I always thought full CTO converts to 3200K, 3/4 CTO converts to 3500 or 3600K depending on which brand of gel you use - maybe its a north/south thing:)) But as you said with such a small difference it is really a matter of taste.
Speaking of gel brands which is just as important a topic- all the gaffers i have worked with tell me that Lee and Calcolour are the most consistant roll to roll. Other brands are less consistant in their transmission and colour temperature - so be warned, not all CTOs are the same!

kpv rajkumar - 85 is the name of the filter you would use on the camera to convert tungsten film to 5600K daylight. It is the same colour as Full CTO and has the same stop loss so i think you're just confusing the names a little bit.
Hope this helps,
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#6 Brian Drysdale

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Posted 05 August 2006 - 11:31 AM

Actually id have to disagree with you there Brian I always thought full CTO converts to 3200K, 3/4 CTO converts to 3500 or 3600K depending on which brand of gel you use - maybe its a north/south thing:)) But as you said with such a small difference it is really a matter of taste.
Speaking of gel brands which is just as important a topic- all the gaffers i have worked with tell me that Lee and Calcolour are the most consistant roll to roll. Other brands are less consistant in their transmission and colour temperature - so be warned, not all CTOs are the same!

kpv rajkumar - 85 is the name of the filter you would use on the camera to convert tungsten film to 5600K daylight. It is the same colour as Full CTO and has the same stop loss so i think you're just confusing the names a little bit.
Hope this helps,


So did I until I checked the spec from the filter manufacturers. With LEE Full CTO corrects from 6500K to 3200K (mired shift + 159). Roscosun Full CTO corrects from 5500K to 2900K (mired shift +167). Their 3/4 CTO to 3200 (mired shift +131).

A 85 camera filter has a mired shift of + 113 and the 85B + 131.

Of course, the lighting filters may not actually do it in practise, but that those are the manufacturer's specs.
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#7 ChrisConnelly

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Posted 05 August 2006 - 02:13 PM

If you are worried about your hmi being off color then first try replacing the bulb with a fresh bulb. Wait untill the light has come up to temperature and then measure it with a colour temp meter. Add Plus or Minus green if required. HMI's with older bulbs can turn a bit greenish and they do need to be checked regularly. Hope this helps,


Just to note that a brand new HMI bulb will have to be corrected as well, as they burn too blue at the beginning of their "life", closer to 6000-6500K.
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#8 Bob Hayes

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Posted 06 August 2006 - 12:56 AM

HMI vary dramatically from unit to unit and globe to globe. I have a hard time judging color shifts so I will often rely on a color temp meter. I admit I have been caught many times because I was lazy in this procedure. I think in the future I am going to constantly measure and correct the lights. Even to the point of labeling them with tape so I know the correction. HD seems extra sensitive to the green/magenta shift. Seeing it on the monitor makes it easier but it also means if it is not caught it will be a problem.
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#9 kpv rajkumar

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Posted 06 August 2006 - 03:30 AM

Actually id have to disagree with you there Brian I always thought full CTO converts to 3200K, 3/4 CTO converts to 3500 or 3600K depending on which brand of gel you use - maybe its a north/south thing:)) But as you said with such a small difference it is really a matter of taste.
Speaking of gel brands which is just as important a topic- all the gaffers i have worked with tell me that Lee and Calcolour are the most consistant roll to roll. Other brands are less consistant in their transmission and colour temperature - so be warned, not all CTOs are the same!

kpv rajkumar - 85 is the name of the filter you would use on the camera to convert tungsten film to 5600K daylight. It is the same colour as Full CTO and has the same stop loss so i think you're just confusing the names a little bit.
Hope this helps,

Steve,thanks for clarifing that for me. from now on i'll not order, " 85 that HMI!", when it actually should be," "Full CTO that HMI ! ".Sometimes, i do interchange these two nomenclatures on a snap, which is not accurate. thanks again.
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#10 Jonathan Benny

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Posted 06 August 2006 - 03:49 AM

kpv rajkumar - 85 is the name of the filter you would use on the camera to convert tungsten film to 5600K daylight. It is the same colour as Full CTO and has the same stop loss so i think you're just confusing the names a little bit.
Hope this helps,


85 gel exists (rosco) and it is different from Full CTO (rosco) in specs. Hold them up side by side to a light and see if they look exactly the same.

AJB
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#11 Chris Pritzlaff

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Posted 06 August 2006 - 04:06 AM

I have found that CTS and CTO combined on an HMI seems to match to tungsten better than just CTO. Anyone else find this, or is it just a personal preference?
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#12 kpv rajkumar

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Posted 06 August 2006 - 05:59 AM

So did I until I checked the spec from the filter manufacturers. With LEE Full CTO corrects from 6500K to 3200K (mired shift + 159). Roscosun Full CTO corrects from 5500K to 2900K (mired shift +167). Their 3/4 CTO to 3200 (mired shift +131).

A 85 camera filter has a mired shift of + 113 and the 85B + 131.

Of course, the lighting filters may not actually do it in practise, but that those are the manufacturer's specs.

Thanks for the info, Brian. I checked my swatch books too. The mired values of Lee's Full CTO & that of Roscosun's do differ, negligibly though.
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#13 kpv rajkumar

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Posted 06 August 2006 - 06:27 AM

85 gel exists (rosco) and it is different from Full CTO (rosco) in specs. Hold them up side by side to a light and see if they look exactly the same.

AJB

Is it Rosco's 'FULL CTO' vs Rosco's 'HMI To TUNGSTEN' that you're talking about, AJ? (Because my swatch book does'nt have any actually marked '85'). Both convert Daylight to 3200 K clean. But, while the former transmits 55.4%, the latter does 58.2%.Thank you!
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#14 Brian Drysdale

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Posted 06 August 2006 - 06:27 AM

Thanks for the info, Brian. I checked my swatch books too. The mired values of Lee's Full CTO & that of Roscosun's do differ, negligibly though.


I wouldn't worry about those differences.

Matching in the half way world between full daylight and tungsten is even more confusing with the CTB working in 1/4s and the CTOs seemingly in 1/3s. I expect that's why Rosco brought out the 1/3 CTB which converges with the 1/2 CTO at 3800K. Assuming 3200K and 5500K light sources respectively.

Hmmm... pity I sold my colour temp meter to one of the local gaffers.
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#15 kpv rajkumar

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Posted 06 August 2006 - 09:09 AM

I have found that CTS and CTO combined on an HMI seems to match to tungsten better than just CTO. Anyone else find this, or is it just a personal preference?

wow, noted for future guidance, chris ! thanks a lot, rk
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#16 kpv rajkumar

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Posted 06 August 2006 - 09:48 AM

I wouldn't worry about those differences.

Matching in the half way world between full daylight and tungsten is even more confusing with the CTB working in 1/4s and the CTOs seemingly in 1/3s. I expect that's why Rosco brought out the 1/3 CTB which converges with the 1/2 CTO at 3800K. Assuming 3200K and 5500K light sources respectively.

Hmmm... pity I sold my colour temp meter to one of the local gaffers.


Brian, was it a Bogen color temp meter ? must be good.
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#17 chris schaller

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Posted 12 August 2006 - 11:23 PM

has anyone else had problems with balancing to litepanels? i never get a ntural light out them.
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#18 Henry Chung

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Posted 13 August 2006 - 06:50 PM

has anyone else had problems with balancing to litepanels? i never get a ntural light out them.

If there is no color meter, is it possible to use a digital camera with full manual controls to monitor the color change ?

Some cameras do have manual color temperature adjustment in 100 deg kelvin.

Henry Chung
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#19 Evan Walker

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Posted 13 August 2006 - 08:28 PM

This was very helpful information, Thank you
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#20 Brian Drysdale

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Posted 14 August 2006 - 08:22 AM

Brian, was it a Bogen color temp meter ? must be good.


No, it was a Minolta Color Meter II - it was great for those greens.
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