How To: Fill flash with a manual off camera flash

Discussion in 'Beyond the Basics' started by GerryDavid, Oct 11, 2004.

  1. GerryDavid

    GerryDavid No longer a newbie, moving up!

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    Im in a lighting techniques class and one of the assignments is fill flash. Either im dense or when the teacher explained how to do this it didnt sink in. I think he expects us all to use light meters or something. I just dont get it.

    the first part of the assignment is to have the light source *sun* 90 degree's to the camera, so to the side of the object. This should make one side bright and the other side dark, of the object.

    the 2nd part is to use the flash to fill in the darker area, so that its 1 or 2 stops less than the bright side.

    For the first part I used something like F8 @ 3 seconds. I used a regular 60 watt house light that was right next to the object. *the object was a carebear stuffed animal*

    the 2nd part, the camera/flash was 5 feet from the object, doing the math, the aperature I should use is F22 since the GN is 110 and the distance is 5' using the formula:

    aperature = GN / distance

    But this is for when the flash is the main source of light, so the ambient light shouldnt interfear with the exposure. But I just want the flash to be "fill". So what I ended up doing was changing the flash from full power to 1/4 power, and bracketed for +/- 1 stop. But I dont like the guess work and would like to know how to do this properly, with out a hand held light meter and with out using the light meter on the flash to control how much light hits the subject.

    Does anyone know how to do this, and explain it so a 5 year old could understand? hehe.
     
  2. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Here's how I do fill flash.

    I could use the flash GN to figure aperture, but I don't really trust it; there must be a sweet spot where the GN is pretty accurate, but for long flash to subject distances it always ends up weak, and for short distances it's usually too powerful. So I prefer using a flash meter, but a little practice with your flash and I'm sure you'd figure out how you need to adjust the GN depending on your distance to subject.

    After I figure the aperture for full exposure I can reduce flash power by 1 stop by either closing the aperture down, or reducing flash power by 1/2. To lose 2 stops you could close close the aperture down 2 stops, reduce the flash power to 1/4, or go -1 f/stop and 1/2 power.

    Once I have the aperture for fill flash exposure, using that aperture I meter the ambient light source (using hand held for me, but you could use your in camera meter) to determine shutter speed.
     
  3. GerryDavid

    GerryDavid No longer a newbie, moving up!

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    Thanks for the words of wisdom.

    I didnt want to touch the aperature because I figure it will also cut down the ambient light and make the picture a bit underexposed, then again for every stop I close the aperature, I could increase the time by a stop, hmmmm.

    I need to buy a light meter, hehe.

    And about the greater the distance, the less acurate the GN is, its actually more acurate, since the equation is using the light as a point light source, the greater the distance the more the light becomes a point source. So when we tested the inverse square law in class, it was more acurate after you get something like 10 feet away from the hand held flash. But it depends on how far your flash can output.

    I tried using the light meter on my flash for the first part before trying to figure it out manually, to see if I could trust the light meter on the flash, hopefully it turned out good.
     
  4. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Yes, use aperture to control the flash and the shutter to control ambient light.
     

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