GN Rating for Speedlights

[beachrat]

For me,the f/1 explanation made sense because the GN is expressed in feet. That made a Vivitar 283 GN 120 feet(probably generous to a fault).
With me so far?
I could not for the life of me understand what "120 feet" had to do with anything until a person with much more knowledge than I simplified it by explaining it the way he did.
It wasn't important in actually using the flash,it just satisfied my curiosity as to why it would have a rating in a seemingly impossible usable distance.

 

[WayneF]

For me,the f/1 explanation made sense because the GN is expressed in feet. That made a Vivitar 283 GN 120 feet(probably generous to a fault).
With me so far?
I could not for the life of me understand what "120 feet" had to do with anything until a person with much more knowledge than I simplified it by explaining it the way he did.
It wasn't important in actually using the flash,it just satisfied my curiosity as to why it would have a rating in a seemingly impossible usable distance.

Well, if you don't or can't use f/1, then 120 feet certainly is an impossible distance.

The point of the GN = distance x fstop is to easily tell you the correct distance for f/8 is GN 120 / f8 = 15 feet. f/1 has nothing to do with it.

Here is the Vivitar 283 Guide Number chart. It does not mention f/1

 

[beachrat]

Wayne,I know that f/1 has nothing to do with the way that the guide number actually works.
But,the way it was explained to me helped me realize exactly how the GN was determined and assigned to a flash based on its power.
Obviously,I can't convey my thought process to you.

 

[WayneF]

Great then, the goal is knowing how it actually works.