Guide Number

Discussion in 'Beyond the Basics' started by ang, Aug 2, 2004.

  1. ang

    ang TPF Noob!

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    I'm trying to decide on a flash for my camera nikon n65. This will be my first flash.

    I'm wondering what importance the different guide numbers are? In the specs of each flash, it seems some guide numbers change depending on the focal length? I understand the larger the guide number, the larger the distance the flash will shoot. Is that all?
     
  2. ksmattfish

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

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    Guide Number divided by distance to subject equals the aperture for correct exposure.

    Example: GN 110 (ISO 100/feet) divided by 10 feet = f/11 (for ISO 100)
     
  3. Daniel

    Daniel TPF Noob!

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    That belongs in the sticky at the top :wink:
     
  4. ang

    ang TPF Noob!

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    So what min. guide number should I look for in a flash if I want to do some portraits with bounce flash?
     
  5. ksmattfish

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

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    Shrug? That depends on your film speed, distance to subject ( for bounce estimate total distance of the bounce, and then open up the aperture at least one stop depending on what you are bouncing it off of).

    I like to go with the most powerful I can afford. You can always cut down power, but you can't make the flash more powerful. I like GN 120.
     

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