Mobile Flash: Your Mobile Studio
Entry- and enthusiast-level DSLRs usually include an on-camera flash which pops up on demand or when using auto mode and shooting in low light conditions. Out of necessity, the flash is physically positioned only a few centimetres away from the lens, which causes a few problems, including ‘red eye’ and harsh, flat lighting. The flash emitted typically overpowers the ambient light, resulting in your subject looking like a rabbit caught in a car’s headlights. In addition, any reflective surfaces in your scene which are parallel to the camera will end up recorded as areas of white glare.
Although there are professional photographers (like Juergen Teller) who have developed a unique style around using on-camera flash, these images are notable for how unflattering they are. As he regularly photographs celebrities, the appeal of the shots is that the subjects don’t appear to be professionally photographed, giving the viewer a feeling of a private image taken by a close friend. For the majority of photographers, however, the main priority of a portrait is to flatter the subject, which is much more easily achieved with off-camera flash.
In low light situations, instead of resorting to on-camera flash, try raising the ISO, slowing the shutter speed and/or widening the aperture to let more light in. Experiment with other light sources – even a street light or a table lamp. If you end up using on-camera flash as a last resort, stick a layer of masking tape or white fabric over the cover of the flash to diffuse and soften the light slightly.
Flash guns offer many advantages over fixed on-camera flash. Their larger size means they can pack in more power, while providing you with accessible options to adjust and control that power. Their adjustable heads mean that the light can be bounced off walls, ceilings and other surfaces rather than just firing straight at your subjects.
Some have in-built or add-on diffusers, which soften and spread the light, and small white pop-up cards that reflect catch-lights into your subjects’ eyes even when the flash is angled upwards or to one side. You can buy mini soft-boxes and umbrellas for flash guns, enabling you to recreate flattering studio-style lighting on location, while still being much more portable.
Flash guns slide into what is called a ‘hot-shoe’; a metal mount positioned on the top of your DSLR which transfers data between the flash gun and the camera. A lever on the back of the gun locks it into place, ensuring it won’t slip off again. On the back of the flash gun is an LCD screen that shows the active mode, the effective range of the light output with the current settings and the camera and lens set-up.
Flash gun modes
The most common modes on flash guns include:
Through the lens (TTL) auto mode
The camera uses through the lens flash metering to judge how much flash is required to make a correct exposure. If necessary, you can use flash exposure compensation (indicated by the same plus and minus sign used on most cameras to indicate exposure compensation) to quickly increase or decrease the amount of flash that’s fired.
Red eye mode
Red eye is caused by flashlight reflecting off the inside of a subject’s eyeball; in low-light situations where you are most likely to use flash, people’s pupils expand to let more light in, making the reflections worse. In this mode, the camera fires several bursts of flash before the exposure is made in order to shrink the subjects’ pupils, helping to reduce the effect of red eye.
Slow sync mode
Uses a slower shutter speed to capture ambient background light as well as the subject, making this a good choice for twilight and evening portraits. However, watch out for camera shake and be aware that the flash fires at the start of the exposure. This means that if your subject moves, their position at the start of the exposure will be frozen by the flash, with their later movements recorded as blurred trails. This can look odd, as you would expect the movement trails to show the earlier movements, with the final position of the subject captured most prominently by the flash.
Second/rear-curtain sync mode
Uses a slower shutter speed to capture ambient light, but also addresses the movement trail issue mentioned above, as the flash is fired at the end of the exposure instead of at the beginning. The name comes from the physical process that takes place during an exposure – a ‘curtain’ draws back to allow light to reach the sensor, then a second follows it to block out light again. In this mode, the flash is timed to burst just before the second curtain moves into place.
Flash off mode
In automatic exposure modes, the camera will default to using flash whenever light levels are low. Selecting this mode disables this function.
Zooming the flash
Flash guns use the focal length information from the lens to concentrate the beam of light before firing, minimising the wasted light that would be spread over a wider scene when a longer focal length is used, and giving the flash a longer reach. This also makes the light more controllable when bouncing it, as setting the flash to its longest zoom setting will ensure it becomes a narrow tunnel of light, rather than an arc, reducing the amount that spills elsewhere.
Taking flash guns off camera
Cable connectors and wireless trigger systems mean that you can just as easily use flash guns completely off-camera, even using multiple flash guns at once, increasing the number of effects you can use them for. Slide a trigger into the hot-shoe instead of a flash gun, and it will fire the flash remotely using radio or infrared signals in time for when the camera makes the exposure. Alternatively, with one flash gun on the camera, set another to ‘slave’ mode and it will fire as soon as it senses the burst of flash from the ‘master’ flash gun.
Your positioning and choice of power settings for the flash guns will determine how flattering the light is. Use the same principles as those set out earlier for studio flash and, whether you are relying on a single flash gun or have several that you can position around your subject, you will be able to recreate similar effects on location.
For example, you can use a large, white, matt surface (such as a room divider or neutrally painted wall) to replicate the effect of a giant studio softbox. When you point light at a matt surface, the amount of light reflected from it is the same in any direction, no matter what angle the light is coming from. This is why you can see images on modern overhead projector screens, no matter where you are sitting – the light entering your eyes is the same from all angles. This creates a similar end result to using a softbox, which bounces light around in all directions inside, so it becomes soft and non-directional.
Simply position your subject as you would if the surface was a softbox in a studio (at a 45 degree angle, or behind the camera, for example), then fire the flash towards that surface, using the maximum zoom setting on the flash to minimise spillage. If using a wall behind the camera, be aware that the shape of your body will block light, so allow some distance between yourself and the subject to avoid shadowing them. Depending on the power of your flash and the distance between your subject and the surface you are using to bounce the light, you may need to widen your aperture, raise your ISO or use a tripod to achieve a correct exposure which doesn’t suffer from camera shake.
If you have a second flash gun, you can aim it at the same surface to double the flash output, use it on a lower power setting aimed towards the shadowed side of your subject as a fill light, or angle it towards your subject’s hair to add depth and texture to the image. Alternatively, position it behind your subject, pointing towards their back to add a rim light that will lift and separate your subject from the background. This is particularly effective on very overcast days, when the background and subject are both under similar lighting conditions. Remember that the main flash gun will need to be at a higher power setting than any secondary light sources, and higher still if used with a light modifier which will diffuse some of its power.
When using multiple flash guns, take test shots of the effect produced by each one individually so you can check and balance their eventual effect on the final image.
Remember that coloured surfaces reflect coloured light, so stick to reflecting light off white ones to avoid adding unwanted tints to your image.
Make it manual
As with camera settings, leaving your flash in an automatic mode means you lose out on creative control. Although through the lens (TTL) flash metering gets it right most of the time, it can fail in backlit situations, when the scene is highly reflective or when the backgrounds are very light or very dark. If you don’t know your kit well, you won’t know how to correct its output in these situations, which is risky. Instead, spend time experimenting with your flash gun until you can accurately predict what settings will create the desired effect in different situations.
Be aware that you will need to use a shutter speed within the camera’s flash sync range. Depending on the make of your DSLR, the top shutter speed available to you will either be 1/200s or 1/250s; anything faster and your image will have a black band across it, where no detail is recorded. This is because one of the two curtains that open and then close the shutter were in motion at the time the flash was fired, and they have blocked light from the burst of flash from reaching the sensor at that point in the frame.
Sometimes, a shutter speed of 1/200s or 1/250s is too slow, especially if you are using flash to fill-in shadows on a bright day. Even at the lowest ISO and smallest aperture settings, the image would be overexposed. To remedy this, some flash guns offer a high speed sync (HSS) mode, in which the flash is repeatedly fired as the curtains move across the sensor, enabling you to use faster shutter speeds and wider apertures than you would be able to normally. To avoid overpowering the scene, especially when using a wide aperture, simply turn the power of the flash gun down, by using the manual settings or the flash compensation control.
Flash gun power and range
Flash guns have a guide number (GN), which indicate its maximum power when used at its narrowest setting. For comparison purposes, GNs state the distance that the light from a flash gun will reach when using ISO 100. Divide the GN by the aperture you are using to get the maximum distance the flash can reach, when fired directly towards the subject. For example, a GN of 40, divided by an aperture of f/4, means you can be up to 10 metres away. Change the aperture to f/8, however, and you’d need to be no more than five metres away.
These calculations are complicated by the fact that most of the time you will be taking advantage of a flash gun’s adjustable head to fire the flash indirectly at your subject or reducing its output by adding a diffuser, in order to make the light more flattering. When used in this way, flash guns will only be effective across fairly limited distances of a few metres.
Note also that when using your flash gun at its maximum power setting, it will take longer to ‘recycle’ (which means the time taken for it to become ready to fire the flash again), and will use the batteries up quicker.