The meaning of Flash Zoom

What does Flash Zoom mean?

Oskar wanted to find out what the zoom setting on his Godox Speedlite TT585 really means. This speedlight allows setting a zoom value from 20 mm to 200 mm. Question: What does the zoom setting of the speedlight do?

Here is the simple test setup: The flash F is pointed at a white wall and placed at a distance b. The camera C is equipped with a flash trigger (Godox XPro) and placed at a distance c to the wall.

Result: At 24 mm the light cone beam is the widest. And so the lighted area on the wall is the biggest. With increasing zoom factor the light beam is narrowed down and the lighted area gets smaller.

Conclusion: The zoom setting of the speedlight controls the size of the light beam. Small zoom values are equivalent to wider beam angles, big zoom values narrow down the beam size.

If you want to use your speedlight in a softbox you should always set the zoom factor to the smallest value to maximize the lighted area. This leads to the next question: What is the maximum size of softbox that can be used with speedlights?