how do you calculate fill flash?

Discussion in 'Lighting' started by RobC, Dec 23, 2007.

  1. RobC

    RobC Member

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    If you are shooting outdoors in bright overhead sunlight and you want to use fill flash to reduce facial shadows, especially under the chin, how do you calculate how much flash to use on a manual camera. i.e. a camera with no flash metering.
     
  2. Dave Miller

    Dave Miller Member

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    I would use an ISO rating of one to two stops higher for the flash than that used for the camera. The idea being to have the flash “under expose” the subject.
     
  3. Nick Zentena

    Nick Zentena Member

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    Meter the scene. Then set the auto mode on the flash one or two stops below that. So if the scene was say F/8 you'd set the flash to F/5.6. Or to whatever level of fill you'd want. Set the camera to whatever you metered the scene to be. F/8 in this case.

    You can also play with the film speed on the flash if the flash doesn't have enough control. So one stop of fill would mean telling the flash you're using a one stop faster film. But then you need to set the F/stop to what is on the camera.
     
  4. RobC

    RobC Member

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    Methinks some practice at this is required to find out what I want because at the moment I just don't know. I guess it depends on how deep the shadows are relative to the rest of the face. But I can see that giving two stops too little flash would change the shadows greatly but make maybe only a 1/3 or less of a stop difference to the higher values.
     
  5. wfe

    wfe Member

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    I would suggest a bit of practice which is what I did the last time I needed fill flash outdoors. Someone once taught me that the flash will never be as bright as the sun so it's not as difficult as it may seem. I can't remember what settings I used but it all worked out very well.

    Cheers,
    Bill
     
  6. Les

    Les Subscriber

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    For manual flash exposure - I prefer to leave the ISO at the correct value for the film and cut strobe power e.g. 1/2 1/4/1/8 1/16th power. Two stops under is equivalent to 1/4 power. Then you don't have to remember ISO or set the wrong value - just go back to full power on the strobe.
    Les
     
  7. JBrunner

    JBrunner Moderator Staff Member Moderator

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    I have found with the flash I have, and a diffuser in place, it is pretty hard to over do it. Sometimes, on an overcast day or in shade, I will set the flash and exposure up, and let the background fall off. It cam make for an intersting effect when shooting people, especially on chrome. Sort of gives them their own glow.
     
  8. brian steinberger

    brian steinberger Member

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    When you say meter the scene, is this at a particlular shutter speed, like 1/125?
     
  9. OldBikerPete

    OldBikerPete Member

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    As others have said, two stops underexposed for the flash fill is a good place to start.
    Just don't overdo the flash, particularly if you have a dark or shaded background as the result can look a bit too 'artificial' for want of a better word.
     
  10. Jeffrey A. Steinberg

    Jeffrey A. Steinberg Member

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    Well, yes and no. Take an incidence meter and hold at the subject facing the lens and meter it. Ones of the combinations will be 1/125 (or it could be)
    as well as other f stop/shutter compinations.

    I hope that answers your question.
     
  11. cowanw

    cowanw Member

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    But you must always meter at a shutter speed that synchs flash with your camera, usually 1/125 ( or 1/60 or 1/250 depending on make) (assuming a focal plane shutter)
    Regards
    Bill
     
  12. haris

    haris Guest

    Meter scene using flash sync speed of your camera and set flash one to two stop faster than your lens. For example, your camera have sync speed of 1/60, and you use ISO 100 film. So, you meter needed aperture for your 100 ISO film and shutter speed of 1/60. And for example, you get f11. So, you set your lens to f11, and you set your flash to f8 or f5,6 (you "tell" that is you "lie" to your flash as you set lens on those openings, but in fact you set lens to f11). That is the way if you have flash with manual setting. If you can not set your flash, that is if flash is automatic, or allways fire full power, you can move flash away from subject, or place something over flash head, like white tissue or "milky white" plastic,which will lesser flash power. For example, StoFen plastic diffuser reduce flash power by 1,5 stops, and diffuse flash light, so flash light is not that harsh as without diffuser.
     
  13. Carter john

    Carter john Member

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    If you have an auto setting on your flash (not TTL), this is what I do (film):

    1. Check flash unit auto settings f stops, choose.
    2. Set camera to 1.5 stops closed from chosen f stop AND then set shutter for ambient light.
    3. Shoot, if it is a fill flash situation.
     
  14. Brandon D.

    Brandon D. Member

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    Incident light meter.
     
  15. jime11

    jime11 Member

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  16. Francis in VT

    Francis in VT Member

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    Fill Flash a little OT

    While in the service I was not in the Photo section.
    A semi was involved in an accident and had a problem with one of the wheels of the trailer.
    An official base photographer came out with the 4x5 Graphic the side flash with the 7" reflector and inserted what looked like a #22 bulb. It was a bright Sunny day but there was a slight shade under the trailer. He was about 4' away when he took the picture. I don't think he was using color as it was 1954 and the film might have been Super XX or something like that. I can only imagine the density of the negative and how long it took to print it.