Anyone have a good webpage RE guide #'s.....

[SeanH]

......and how to do the math. I used to know how to figure it but I forgot.......Guide #/ISO/f-stop??.......damn why can't I remember it....I knew it in High School....in 1980.....LOL

[Photonak]

......and how to do the math. I used to know how to figure it but I forgot.......Guide #/ISO/f-stop??.......damn why can't I remember it....I knew it in High School....in 1980.....LOL

Quite simple. Get a GN for the flash, for you film speed. Typically they are given as GN 120 ISO 100, ft

Assuming you're shooting with ISO 100 film, or digital camera setting, you divide the GN by the f-stop to get the distance.

Dist=GN/f-stop

Photonak

PS Many GN's are inflated, so you should take a few test shots, if that's what you'll be using. Then mark the flash unit with the GN you want to use.

[scottbergerphoto]

At ISO 100 Distance =GN/f stop
for ISO 200 multiply by 1.4
for ISO 400 multiply by 2