GN Need Help Please to understand Distance Flash to Subject.

billh1401

I shoot with a Canon T3i, and use Yongnuo YN 565EX ETTL Flash. I am really trying to learn to use Manual Flash to become proficient at portraits inside and outside. The reason I am asking you about this information is because I like your thought process of making things easy with shortcuts. I believe in the old saying KISS (Keep It Simple Stupid). That is what I try to live by with my photography. I would like to be able to keep it simple for my Flash Photography and not be fumbling around wasting time.

My question is this, manual for my Flash says my GN is 58 or am I totally confused. If I am trying to figure out the proper distance of Flash from subject by the Formula of the GN you presented in you book "Off-Camera Flash",
GN = DISTANCE X APERTURE
Could I just reverse the formula and do: Distance = GN/Aperture
Exp: (Chart) for a zoom of 35 and a power output of ¼ @ ISO of 100
19.5(m)/64(ft) & an f/8 Aperture

64/8 (f/8) = 8ft
Distance = 8 feet

Jamesev

If GN is 58 then at f8 distance = 7.25 ft

Angelo69

Hi

I think you are just twisting yourself in knots thinking about numbers etc. You should concentrate on the factors which effect manual flash: ISO, Fstop, power and subject to flash distance.
Play around with these on your camera, and you will see the relationship when you change one, some or all of these things. Set up a small static test at home and see what happens. The penny will drop soon.

Neil vN

Bill ... make sure you go over this article too:

http://neilvn.com/tangents/2012/03/08/tutorial-how-to-use-the-guide-number-of-your-flash/

Neil vN

billh1401 said: Could I just reverse the formula and do: Distance = GN/Aperture

Yup, that's how it works as a basic mathematical formula.