Flash Color Temperature Issue

Discussion in 'Lighting' started by Pasto, May 19, 2012.

  1. Pasto

    Pasto Member

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    I'm starting a new project soon that will involve shooting interiors with Portra 400 sheet film and flash. Prints will be RA4. I checked the color temperature of my flash and found that it varies from about 4400K to 4800K depending on the output. The meter suggests using an 82A or 82B cooling filter to balance the flash light. The specs for portra 400 suggest no filtration for daylight or flash. I'm wondering if 4400K to 4800K is close enough to the 5500K this film is presumably calibratred for? Is it impotant to filter in this case? Thanks in advance for your advice...
     
  2. ic-racer

    ic-racer Member

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    I'd think you should be able to adjust the coloration when printing. If you are going to shoot a gray card and match that, don't alter the flash output after that.
     
  3. markbarendt

    markbarendt Subscriber

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    I'd say generally that it's going to boil down to personal preference and whatever makes your printing easier.

    The wild cards are the ambient light and the surfaces you'll be bouncing off.

    Another option you may consider is using gels on the flash gun(s). If for example you are using a nikon speed light in "A" mode this can get you better exposures because the flash gun measures it's own output rather than the camera. The flash gun doesn't "see" the filter.
     
  4. Pasto

    Pasto Member

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    There will not be any ambient light as the flourescents will all be turned off prior to exposure. Also, I'm using speedotrons and I've thought about geling them instead of filtering the lens....
     
  5. markbarendt

    markbarendt Subscriber

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    Sounds like its time to test a few sheets.
     
  6. Bob-D659

    Bob-D659 Member

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    Run a roll thru a 35mm or 120 format camera, lower cost than a few sheets of film.
     
  7. Leigh B

    Leigh B Member

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    No. 4400K is halfway between daylight (5500K) and incandescent light (3200K).

    Filtration is certainly appropriate. You can bandaid it after exposure, but there's no substitute for getting the negative right in the first place.

    You should check your strobes. They're way off; should be 5500K-5600K.

    - Leigh
     
  8. Pasto

    Pasto Member

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    I'm wondering if it's my color meter. My metz 45CL4 comes in at about 4800K......
     
  9. Leigh B

    Leigh B Member

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    It's difficult to get a consistent color temperature reading.

    I just took my Gossen Color-Pro 3F outside to read sunlight, with thin clouds covering most of the sky. It's 4PM daylight saving time here.
    Depending on exactly where I pointed the sensor, I got readings from 5780 to 5910. That number would have been lower in direct sunlight.

    The CT reading is actually just the ratio of red to blue. The green component of white light is not evaluated at all.
    Most modern CT meters include a separate channel to read green and suggest magenta/green filtration to balance it.

    - Leigh
     
  10. Pasto

    Pasto Member

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    I hear you Leigh. I just stepped outside and took some readings with my Minolta Color meter II. I got between 5200 and 6000 depending where I pointed it (It's sunny with no clouds today here). My meter is the older version that requires the incident sensor head to be swapped with the flash sensor head for flash readings. I was just surprised that my speedotron 102 flash heads were so far away from 5500. The readings from the flash heads were quite consitent from burst to burst. I just sent email to speedotron to see what they think. My understanding is that these flash heads should measure closer to 5700K, and that the new UV coated bulbs are closer to 5500K.....
     
  11. Pasto

    Pasto Member

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    Oh, forgot to mention one more thing. My Minolta suggests no magenta/green filtration but about -30 mired red/blue filtration for the speedotron flash heads.
     
  12. Leigh B

    Leigh B Member

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    It sounds like your meter is working properly. That's a good reliable CT meter.

    Drop in CT for flash units is usually caused by material being deposited inside the tube as it's used.
    The coating usually has a slight reddish cast, which lowers the CT of the flash.

    I used to be a warranty service station for Novatron, and had occasion to replace flash tubes for that reason.

    - Leigh
     
  13. Leigh B

    Leigh B Member

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    If that's really the only issue, you could correct it inexpensively using Rosco gels over the strobe heads.

    - Leigh
     
  14. Pasto

    Pasto Member

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    Just got word from Speedotron and, as suggested by Leigh, it is normal for older bulbs to drop in color temperature. I either get new bulbs or gel the heads. My meter suggests a wratten 82B as the proper correction filter. Any idea how this converts to CTB filtration?
     
  15. Leigh B

    Leigh B Member

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    Hi Pasto,

    I have no idea how to convert from Wratten numbers to Rosco product codes. Perhaps someone else knows.

    You know the gel will be a light blue. I would buy a pack of same, preferably in assorted densities, and experiment. You can always stack two or more if needed.

    - Leigh