Flash Photography - Zoom Flash

Many photographers are puzzled by the concept and practice in relation to zoom settings on flashguns.

No matter whether you have a brand new flash with automatic, internal zoom or an older flash gun that has to be manually set, the goal is the same, to match the angle of flash coverage to the lens you are using.

My advice to you is to fully understand this simple concept. Even if you are using fully automatic units there may come a day when you have to set the zoom manually, it is then you need to understand it.

I once nearly ruined a wedding shot by shooting with the lens on wide angle and the flash on telephoto zoom setting. Luckily I noticed this just after taking the shot, and was able to set it up again, don't let it happen to you! I'll explain this further.

A flash sends out a beam of light from a relatively small point source. The width of this beam has to be wide enough to cover the same angle the lens covers. If it does not, you will suffer light drop off in the corners of the photograph, so basically your shots will be dark at the edges.

At the same time, concentrating the beam of light provides better illumination at a distance.

Zoom flashes provide the best of both worlds by matching, or allowing the photographer to match, the angle of flash coverage with the angle of lens coverage. As an example, if you are using a 28mm-135mm zoom lens and have a non-zoom flash that only provides coverage at say a 35mm angle, any photographs taken at less than the 35mm zoom lens range will have darkened corners.

The wider your lens perspective is, the more of each corner will go dark. This is what happened to my wedding shot. At the same time, when you are shooting above the 50mm zoom lens range, you would be wasting progressively more light as you zoomed the flash further out. While this would not be noticeable in the photographs, it would limit your choice of aperture and require more power to be used because the beam of light would be less concentrated than it could be. That means you'd be lighting a wider area than the lens is actually seeing.

A zoom flash solves these problems by matching the light coverage to the lens coverage. I prefer flashes with a manual zoom feature, or at least with an automatic zoom that can be overridden, because when bouncing or diffusing the flash I often prefer a setting that does not match the focal length I am shooting at. This will become clearer if you understand the concepts of diffusion and bouncing of flash.

Zoom flash works well with TTL metering because many lenses have an aperture that will vary with the focal length of the lens. I hope this article on zoom flash has helped.