Jump to content

how to get the correct color from hmi


Recommended Posts

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?

Link to comment
Share on other sites

Guest Stephen Murphy

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,

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

Lee have a filter for converting HMIs to tungsten: http://www.leefilters.com/LPFD.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
Link to comment
Share on other sites

Guest Stephen Murphy

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,

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

  • Premium Member
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

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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!

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

Hi all

 

I realise that there are gaffers and DoPs on this forum who are vastly more experienced than me when it comes to colour correcting sources. Given that, I am very uncertain about recommending using photographic colour temperature meters with discharge sources.

 

Most meters are designed to give accurate readings of tungsten lamps but can be confused by discharge or florrie type lighting. Meters work by taking several (typically three) readings of different colours and calculating the colour temperature from this. The spectrum of a discharge light is full of peaks and troughs and the meter can give incorrect results if one of its measuring points hits a peak or trough.

 

I'd suggest that although the eye may not be good at judging colour absolutely, it is very good at comparison, and could be a more reliable instrument for colour correcting than a meter. If you set up three lights and shine them on a white wall it is obvious if one source does not match the others and requires correction. If one is really green, that suggests it is either faulty or very old and should be replaced.

 

The eye will also give information about colour rendering which a meter will not. Some sources can be the required colour temperature but still over or under emphasise certain colours.

 

I hope this is helpful.

 

Regards

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...