If my theory on the lighting is correct, the angle and size of the light is the same, the formulas I had in my first attempts to calculate out the size of the light circles were backwards..
they were somewhat correct but something isn't good enough.
This new java applet shows the distance from the center to the different whole stops down.
Formula is first start at the center formula being:
Gn / Ft = F
Gn = Guide Number
Ft = Feet from flash to subject.
F = F/stop
After you have the base F/Stop, then I would calculate the size of the F/stop Zone, from the center out.
D = Sqrt( ( Gn / ( F / 1.4 ) ) 2 - ( Gn / Ft )2)
D = distance from center
Gn = Guide Number
Ft = Feet from flash to subject.
F = F/stop
For example:
Gn = 310
Ft = 10
F = 31
D = sqrt( (310/ (31/1.4))2 - (310/31)2 )
D = sqrt((310 / 22.1)2 - (10)2)
D = sqrt((14.1)2 - 100 )
D = sqrt( 198.81 - 100)
D = sqrt( 98.81 )
D = 9.94 (basically rounded to 10 because there are allot of rounded numbers in each step of the calculations)
Then to get the next distance basically use the formula over again just take the previous F/stop and divide by 1.4
F = 31 / 1.4 = 22.1
now we start the formula over again.
D = sqrt( (310 / (22.1 / 1.4)2 - ( 310 / 31 ) 2 )
D = sqrt( (310 / 15.8)2 - (10)2 )
D = sqrt( (19.6) 2 - (100) )
D = sqrt( 384.16 - 100 )
D = sqrt( 284.16 )
D = 16.8 (this calculated out to the 10th decimal place makes the Distance to 17.3)
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