Words and pictures by Peter Bargh.
You may, at some stage, have been disappointed with the pictures you’ve taken with your camera using the built-in flash. This is because the flash on most is only capable of illuminating a subject that's a maximum of three meters away from the camera and the light is also very directional.
You can improve things with a small accessory called a slave flash or by using a slave adapter on any detachable flashgun.
How it works
A slave flash works like any ordinary flashgun, so you can use one mounted on the accessory shoe of a camera or connect to a camera using a cable extension, but it also has a sensor built-in that allows it to be triggered from another flash. It can be placed anywhere within the sensor's triggering range or the output of the flash you will use to trigger it. It fires in synchronisation with the main flash that's connected to the camera and can be used as we'll show here to change the way the picture is lit by positioning it in different places. Any camera can be used that has a built-in flash or connected accessory flash, including compacts and SLRs. With digital cameras you have to be careful that it fires at the same time as some have a pre-flash system that fools the slave to fire out of sync.
In the image to the right, a slave flash was positioned behind the guitar and fired at the background to create this unusual background lighting effect.
Why use a slave flash
You could use the slave flash to light nooks and crannies in interior shots where the on camera flash can't reach such as cupboards, alcoves, underneath arches etc. In portraiture it can be used to provide a hair or rim light for a model shoot or a side light for enhanced lighting. You can point it up or down to graduate a background too. It can also be used as a power boost to the built-in flash when you want to shoot at a longer range. You could even use two or three for more complex lighting, but lets keep things simple for this exercise.
Supporting the flash
The flash won't stand up on its own, but will sit comfortably on its side or top. If you're taking things seriously you could buy a mini tripod and a flash shoe adaptor then the flash could be mounted on the tripod and angle to any position you desire. They are usually light enough to be suspended on a nearby door handle or similar using an elastic band.
Achieving the correct exposure is the most tricky part of using a slave flash. The flash built in to the camera works automatically with the camera's exposure meter to ensure the correct level of light. Add a slave flash and the camera has no control over this so you need to either set the slave flash to auto and ensure the camera is working at the same aperture or adjust the slave flash distance so it doesn't overpower.
With a digital camera you can quickly check the LCD after taking a photo to see if the flash is overpowering and then either move it further from the subject or tape tissue paper over the tube to reduce the output. With cameras that have manual exposure control you can be more precise with the aperture and balance the slave with the built-in flash.
Here are a couple of examples of what just one extra flash could produce:
In the photograph on the left it was illuminated by direct flash. But look at the difference if you place the slave flash where the bulb would be. You get a lamp that appears to be on, but without the yellow colour cast that would normally occur.
In the shot of the room, the left was taken with direct flash and it's not powerful enough to reach and deliver a good exposure. The middle shot is lit with just the lamp and it's added the usual yellow colour but it's better than the flash shot although more care was needed when taking the photo as the darker conditions meant a slower shutter speed had to be used. The method used above is applied in the shot on the right. The additional flash has provided a more interesting shape over the sofa and overall a shot with much more character.
With this close up of a toy car the flash is harsh and the auto exposure has made the background wallpaper dark and distracting. By placing a flash out of shot, pointing at the background it's made the car stand out more and has eliminated the various hard shadows caused by the direct flash alone. The base is also better exposed with reflections appearing below each tire and the background is perfectly white. You could add a colour gel (or sweet wrapper) over the slave flash tube to make the background coloured.
In the shot above the left version is with direct flash, the middle has the slave flash firing from above and the shot on the right has the slave flash firing at the background from a low point on the left. It's the best of the three in terms of exposure of the guitar with the bright neck and has avoided the highlight across the guitar body that appeared in the middle shot. The only problem now is that the low angle of the slave flash has highlighted the creases in the backdrop which need addressing. However, this is something you'd be able to check on your camera's LCD screen and adjust your lighting set-up to fix the problem.