Embarrassing question

[mikew_RIP]

I have forgotten how to calculate what power a flash gun would be at say 12 inches with this guide number, Guide Number (ISO 100) : 22-m/72-ft

 

[Eyelight]

I might be a bit rusty on this, so somebody else confirm.

GN = distance × f-number

72 = 1 x f/72 so use f/72 at 1' at full power, or f/36 at 1' at 1/4 power

 

[mikew_RIP]

I might be a bit rusty on this, so somebody else confirm.

GN = distance × f-number

72 = 1 x f/72 so use f/72 at 1' at full power, or f/36 at 1' at 1/4 power

Thanks ime looking at making a macro flash unit,it would be manual with the V2 so wanted to have an idea of the power as i would need to soften the light thereby losing some

 

[Roy1961]

mate thats the sign of old age setting in when you cant remember....... wait what was the question?

 

[WayneF]

Eyelight is of course correct, GN 72 is 1 foot at f/72, or f/36 at either 2 feet or 1/4 power.

A good GN calculator might be useful, www.scantips.com/lights/flashbasics1c.html

 

[mikew_RIP]

Eyelight is of course correct, GN 72 is 1 foot at f/72, or f/36 at either 2 feet or 1/4 power.

A good GN calculator might be useful, www.scantips.com/lights/flashbasics1c.html

Thanks i have book marked that page