Automatic Speedlite zoom might catch you out

Categories: Accessories, Tips and Advice - Tags: Camera, Flash, Lens

Several of Canon’s Speedlite’s have a great feature designed to help you get more range out of your flash, the flash head reflector changes position to tailor the beam of flash to match the lens fitted to your camera. So if you have an EF 24-105mm f/4L IS USM lens on your EOS 5D Mark II then it will be a pretty handy thing. It’s great with other cameras and lenses, but the zoom range of the Speedlite 580EX II is from 24mm to 105mm in automatic mode. By moving the flash reflector and narrowing the beam of light it enables the flash to fire further, often handy with longer focal lengths and greater subject distances. If you like you can still manually change the zoom of the flash either from the flash or your cameras flash menu. The ‘wrinkle’ in the system is that the zoom setting changes when switching between single and multiple Speedlites operation.

Masters and slaves zoom to 24mm

When you put a Speedlite in to master or slave mode, the first thing it does is zoom it’s head to 24mm setting. For a master this means that it tries to spread the control signals for the slaves over a wide area. For a slave I often manually change the zoom to match my lighting intention. Wider setting if I’m lighting with an umbrella and tele setting for honeycomb grids. If you switch a flash from master mode or slave mode back to normal single flash operation the flash head will go back to automatic zoom control, and there’s nothing you can do but remember to correct this.

Let me explain the scenario that nearly caught me out. I was shooting some portraits and using one of Syl Arena’s 10 metre long OCF33 cables and my single flash is on a light stand away from the camera and firing in to a silver parabolic umbrella. From the camera menu I can change all the flash settings including the zoom to match the umbrella. I’ve found that for my silver parabolic umbrella a setting of 28mm works without spilling light round the sides. I’m shooting with the EF 70-200mm f/2.8L IS II USM lens. All is going well, but the sun gets a bit brighter and I decide that I will need a bit more power from the flash. My solution is to add another Speedlite 580EX II in slave mode also firing in to the same umbrella and make the cable connected flash a master. Now I get more power and I did remember to manually set the master and slave to 28mm zoom head setting. Even in bright light the proximity of the slave and master in the same umbrella means the slave can happily ‘see’ the commands from the master.

Changing your Speedlite from master or slave to single flash mode will reset the flash head zoom to automatically zoom to match your lens focal length

A change of location and scene and I only needed a little fill light and it was getting windy so I took the slaved flash off the umbrella shaft (it was bungeed to it!) to avoid it taking a drop to the floor. From my camera I put the cable connected master back in to normal single flash operation mode, and here is where it dropped back to automatic zoom. I’m shooting at over 120mm focal length on the zoom lens and the flash head is zooming to 105mm, my umbrella is now getting a smaller patch of light hitting it and giving me a narrower beam of light on my model, luckily I saw it after chimping a few frames of the new set-up. A quick look at the flash settings from the camera and set the flash manually back to 28mm and all is good.

Canon specifications for flash guide numbers are based on the flash head being zoomed to the longest focal length. You won’t get a guide number of 58 if you set the zoom to 24mm on a Speedlite 580EX II.