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Setting flash manually

  • 14-10-2010 11:21pm
    #1
    FoxT
    Closed Accounts Posts: 4,204 ✭✭✭


    I've been using radio poppers a while now with off-camera flash, and I have been challenging myself to get the flash power setting right the first time, without using the distance scale.
    Here is my current MO.

    At 50mm f/1.4 the flash has a range of 30 metres at ISO 100. The GN therefore is 42.

    If I want to shoot at f/4, and the subject is say 2 metres away from the flash ( still at ISO 100) then I set the flash zoom at 50 mm and I know the GN I need is 8.

    Unfortunately the manual power settings are 1/2, 1/4, 1/16th etc. To me, it would make so much more sense if you could just dial in a GN instead of a power level.

    So now I have to do some math. 8/42 = 1/5 approx. Because of the inverse square law, I therefore need 1/25th power. This is pretty close to 1/32, so that is my starting point.

    This actually works reasonably well, it gets me to within a stop of where I need to be, depending on if I am bouncing the flash, etc. but I am wondering - is there an easier way to do it?

    Thanks,

    FoxT


Comments

  • #2
    .Longshanks.
    Registered Users, Registered Users 2 Posts: 5,718 ✭✭✭.Longshanks.


    Easier - Trial and error
    After a few weeks (months!) practice I can now get it with 80-90% of what i'm after 1st time.

    the tried to look into the inverse square law.....i kinda get it but can't be bother with it TBH!


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