Correct 5000K to 5600K

[Bob Gruen]

Has anyone tried to correct 5000K fluorescent to 5600 (HMI)? A quarter blue takes 3200K to 3500K, would it get 5000K in the neighborhood of 5600K? Would a third blue be closer (3200K to 3800K)?

Is the kelvin scale linear? If it is the third blue would seem right, if not the quarter might be the correct choice.

Anyone done this?

Bob

 

[Ryan Patrick O'Hara]

The EXACT way is to correct color temperature is to use 'Mireds'.

To find your Mired value divide one million by your color temp in degrees kelvin.

Example:

Mired Value= 1,000,000/5000k

Mired value= 200 <------This is your light.

Mired Value= 1,000,000/5600k

Mired Value= 178.5 <-----This is your 5600k/HMI


Your light is 200 and you want it at a 178.5. You will need a gel with a mired shift of about -21.
(mired shifts with negative value is CTB, mired shifts with positive are CTO)

Take a look at this website. Most professional gel companies will tell you the mired shift of the correction gel.
http://www.rosco.com/us/filters/cinegel.asp?order=so&display=11
http://www.rosco.com/us/filters/cinegel.asp

Funny thing is, it looks as if your best choice is a quarter blue (mired shift of -30). I never took the time to see if the scale is linear, I just use mireds.

If you are really being this exact with your color temperatures then you will definately need to get yourself a color meter. I say this because daylight is usually never exactly 5600k and HMI's (depending on the age/use of the bulb) are usually never spot on 5600k either. See what I mean? Sunlight can reach up into the 7,000k's

 

[Indywannabe]

Hey Bob. Just curious...are you trying to match scenes that used different fixtures or just mixing fixtures on the same scene.

(btw: good info Prodigy)