Some Help Understanding Guide Numbers?

[guyharrisonphoto]

Hi, what is the relationship in brightness between guide numbers? In other words, how much brighter than GN 20 is GN 24, or 32, or 40. Is GN 40 twice as bright (one stop?).

Thanks,

Guy

 

[DazedAndConfuzed]

As indicated in the other forum, GN's strength is proportional to square of its number. Thus GN of 28 is 2x as strong as one with GN of 20 (28^2=800, while 20^2=400). Just like the f/stop, both these numbers relates to the surface area (that's why we are using square of its number, since area is X*X), whether it is surface area being light by a strobe, or aperture area that the light is being let thru.

 

[guyharrisonphoto]

Thanks Lwang, your post on wetpixel was very helpful. I posted a question on wetpixel regarding using two connected ys-01s as a "single" strobe for each side of my dual strobe setup, as opposed to single YS-D1s on each side. I will throw out that idea here as well.

 

[mjh]

Two 01s vs. one D1: Part of the question is dealing with Backscatter for CFWA/WA. Two strobes are better than one when trying to light large subjects and keeping backscatter to a minimum. Especially if you are dealing with very wide lenses that let you get close to the subject. So if I was going to be shooting big subjects, I could get close to, with a fisheye lens, I would go with two 01s vs. the one D1.

The other part of this is future upgrades. Cameras come and go it is lighting that we keep, more is better. No doubt two D1s are the ideal and far superior, but you can buy 4 01s for the price of two D1. If a second D1 is in the "not too distant future" then go with it and add the second D1 when the budget allows.