420ex GN question

I have a 420ex, and I know that the GN changes depending on flash zoom. For example at 24mm zoom setting in the flash, the GN is 23 in Meters. At 50mm zoom setting, the GN is 34.

This tells me that you're conentrating the light which makes it go farther, a factor in the Guide Number calculation. This is not to say though, that if you had the 50mm zoom setting and bounced the flash into an umbrella that it would have more light output than if the flash were set at 24mm. Correct?

(ps. i know that if i use the 420ex off camera it auto zooms to 24mm).

tia

sg

I think you have it right.

The GN only applies when you aim it at your subject. If you bounce it off something, it doesn't mean much.

It's hard to say what zoom setting will give you the most range when you shoot into an umbrella, but generally you want to use the widest setting to fill the umbrella so that it can do what it's designed for, which is to make the light source larger.

cool