Is there an easy way to understand inverse square law?
Let's call
I=actual intensity of light
O=Flash output
d=distance to subject.
The law says that I=O/(d squared)
If the distance doubles to 2d, then you have to divide by (2d)squared. So
I=O/(2d)squared=O/4(d squared), So the intensity falls by a factor of 4.
If the distance trebles to 3d, then you divide by (3d)squared=9(d squared), so the intensity falls by a factor of 9.
And so on.
KCook wrote: You look like you are tracking a wounded gazelle
John Landolfi wrote: Let me try:
Let's call
I=actual intensity of light
O=Flash output
d=distance to subject.
The law says that I=O/(d squared)
If the distance doubles to 2d, then you have to divide by (2d)squared. So
I=O/(2d)squared=O/4(d squared), So the intensity falls by a factor of 4.
If the distance trebles to 3d, then you divide by (3d)squared=9(d squared), so the intensity falls by a factor of 9.
And so on.
FYI to the original poster there is a video in the tips section here with Mark Wallace that covers this too. 
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