If you’ve used a Speedlight then you’ll have spotted the zoom setting which can be used to make the spread of light from the flash match the angle of view from your lens. When it comes to on camera flash that’s great news as it helps to maximise t he efficiency of the flash but go off camera and it’s something that can easily get over looked. Setting the zoom for off camera speedlite work is one of the handy tools in a photographer’s bag of tricks. It can be used to shape the light into a tight rectangle or spread it wider and rounder. Most speedlight’s even have a pull out diffuser for a crazy wide spread of light. So what should you do with the zoom setting when you’re shooting your flash into an umbrella or softbox? In a nutshell I tend to zoom out to the wider end of the flashes zoom range but I wanted to see how things changed at different zoom settings so I did a little experiment. Let’s start with the side view. At my Canon 580EXII’s maximum zoom of 105mm the flash is diffused fairly well but it’s noticeably bright in the centre with a lot of fall off at the edges. Things don’t change much even at 50mm zoom but by 24mm zoom the light spread from the umbrella is a lot more even. Flip out the wide angle diffuser and zoom reads 14mm, now that’s wide! The resulting light is amazingly soft and diffused but it’s so wide it actually passes the edges of the umbrella completely! It’s the front view which probably make things clearest. The hot spot at 105mm to 50mm is clear to see. At 24mm the flash coverage is better but at 14mm it’s very VERY even. So what conclusions can I draw from this? Well the obvious one is don’t zoom the flash when using an umbrella or softbox. 14mm looks very tempting but one thing to note is the flash power was roughly a stop less than at 24mm. So I’ll be sticking to 24mm for my brollies but I might consider going for 14mm in softboxes when I can accept shallower depth of fields or higher ISO in my photo.