... The zoom function ranges between i think 24mm and 105mm. What effect does changing the zoom function have on light output? Thanks in advance guys.
As you zoom in (towards 105mm) you concentrate the light and make it stronger so conversely you make the light weaker as you zoom out (towards 24mm).The manual gives you guide numbers at each zoom and power setting, see page 43.
If you don't know how to use 'guide numbers' then look here (bottom of page):