Commercial Photographic Technique – Flash Photography
The humble flashgun can not only help you overcome tricky lighting situations – but also create dazzling fast and slow exposure effects.
In an ideal world we could rely on natural light to perfectly illuminate subjects in every photographic situation. But the simple fact is that the sun’s more likely to light subjects in an inadequate or awkward way. In these situations should you give up and pack away the camera? You’ve got to try and rectify the situation – and one of the most effective tools you’ve got is your flashgun.
A burst of electronic flash can let you continue shooting in low light as well as counteract problematic lighting conditions. It can also capture moving subjects when it’d be virtually impossible using natural light alone and, when mixed with ambient lighting, it becomes a powerful artistic tool. Whether you’re using a built-in pop-up flash or a beefier external gun, your camera’s flash modes will help you take full advantage of all these benefits for your commercial photography.
Automatic
When you switch to auto flash mode your camera will automatically activate flash whenever it deems light levels to be insufficient for a correct exposure. It’s extremely limited because the decision to fire is dependent on the overall brightness of the scene, rather than whether your actual subject’s adequately lit.
Guide numbers
The unit used to measure the power of built-in and auxiliary flash units is the Guide Number. The higher the number the more powerful the flashgun. In technical terms the guide number’s the required aperture at ISO 100 multiplied by the distance (in metres) between the flash and the subject . So for example, a flashgun with a guide number of 38 at ISO 100 will have a range of 13.5 metres at f2.8.
X-sync speed
Because a typical burst of flash is so short, a camera will limit the maximum shutter speed when using flash. This so-called ‘x sync’ speed ensures that the shutter’s fully open when the flash fires. If it isn’t, part of the shutter may still be obstructing the CCD, causing part of the frame to be shielded from the flashlight. The flash x-sync speed of most SLRs is between 1/60th and 1/500th of a second.
Front curtain sync
Often referred to as daylight sync or fill-in flash, this mode lets you force the flash to fire at any time to augment your main light. As well as being a convenient way of illuminating dimly lit subjects such as building interiors, it’s commonly used in portraiture to fill in shadows caused by harsh back, side or top lighting. This creates a softer, more balanced appearance and it’s a great way to add attractive catch-lights to a subject’s eyes. In the hands of a skilled commercial photographer, daylight sync can also be used as a creative tool for highlighting or isolating key compositional elements.
Electronic flash delivers light with almost exactly the same hue and visible spectrum as mid-day sunlight, which is why it’s often referred to as ‘artificial daylight’. At 5,500 degrees Kelvin it has a bluish colour temperature and can therefore effectively be used to cancel out the orange casts caused by tungsten lighting.
Fill-in flash has other major benefits. Because the duration of a typical burst of flash is just 1/10,000th second, you can use it to freeze almost anything on the move – water droplets, somersaulting gymnasts, hummingbirds – you name it. These qualities make daylight sync an invaluable aid for sports, press, wildlife and many other action photographers. Be careful if you scene contains multiple subjects at different distances away. Light intensity falls away with distance, so subjects closer to your flashgun will be more brightly lit than those further away. To be precise, the relationship between light intensity and distance adheres to an inverse square law. So if you double the distance between your flash and your subject, you reduce the amount of light reaching your subject to one quarter.
Slow sync
Slow sync mode fires off a burst of flash at the beginning of the exposure, then holds the shutter open for longer than usual to balance the flash exposure with the ambient illumination. Slow sync effects can look very striking when there’s a big difference in colour temperature between the background lighting and the flash. For example, with a burst of electronic flash you can give a cool blue look to a subject silhouetted against a fiery red sunset. Another benefit of capturing background details beyond the flash range is that the apparent intensity of the flash is softened.
Providing you use a tripod and keep your subject still throughout the exposure, slow sync can produce well-balanced people portraits outdoors in low light or at night. Use daylight sync in this scenario and your foreground subjects will be captured but the background will fade to black. By enabling you to show creatures in their natural surroundings, slow sync can help you to create powerful nocturnal wildlife portraits, too. And as the flashlight reflects from the back of the animal’s eyes it can create a dramatic, luminouos eye-glow.
Rear curtain sync
As with slow sync, this mode provides a longer than usual shutter speed to blur movement and/or capture background detail. The big difference is that the action-freezing flash burst is injected just before the rear curtain closes rather than immediately after the first curtain opens. You can use slow sync to record moving subjects, but rear curtain is far more appropriate for action shots because motion trails are recorded behind the subject as opposed to in front – which often looks peculiar.
Switch to rear curtain when you want to capture light trails behind moving vehicles or add dynamic motion blur effects to sporting or wildlife subjects. You can also create really eye-catching rear curtain, motion blur effects with dancers. In this mode try mounting your camera on a tripod, switching to shutter priority and setting slow shutter speeds manually. As a general rule when using flash, remember not to select shutter speeds faster than your camera’s maximum x-sync speed.
Red-eye reduction
This mode is typically offered in conjunction with auto, first curtain and slow sync. It can be very effective at close range, but do make your subjects aware that around a second’s worth of pre-flashes will fire before the shutter is released and the main flash fired.
More power to you
Knowing when and how to wield your camera’s various flash modes will turn you into a more flexible photographer, but you’ll still be limited if you rely on built-in flash. If you’re serious about increasing the power and versatility of your system then a battery-powered, clip-on external flashgun is a must. They don’t come cheap, though – expect to pay at least £100 for a decent entry-level unit and up to £360 for a model such as the Canon Speedlite 580EX mk2. There’s also a major increase in size and weight to contend with.
So what do you get for the investment? For a start you get a more powerful flash range – up to around 30 metres ( if you want still more power you’ll need a ‘hammerhead’ type gun that attaches alongside the camera). Many external guns also feature tilt and swivel heads that let you bounce the flash off walls, ceilings and reflectors for a softer result. Higher end models also have the advantage of motorised zoom heads that automatically alter the angle of flash coverage to match your lens focal length. With longer lenses the flash output is concentrated into a narrow beam to enable it to travel further, whereas with shorter focal lengths and light’s spread out over a wider area and shorter distance.
Most zoom head flashguns cover the focal length range 24 to 105mm. This means that if you mount a wide angle such as a 17 or 14mm, you’ll get a nasty vignette effect at the edges of the frame. Luckily you can minimise this by fitting a special wide-angle adaptor over the flash window (supplied with many zoom head guns for commercial photography). With out-of-range telephoto lenses, your flash simply won’t be powerful enough to reach the subject. If you still need flash when you’re using long focal lengths to photograph wildlife, for instance, you can buy a flash extender that fits over the flash head and allows you one or two extra stops of light.
Quick as a flash
Another major benefit of external flashguns is faster recycling times. Built-in units can take several seconds to charge up and as many as 20 to recharge, whereas a decent external flash unit should recharge in under a second. What’s more, pro level flashguns offer continuous, high-speed flash, but there’s a downsides – flash output levels can be erratic and units require a considerable time to cool down and recharge. For example, after firing off 15 bursts at maximum output at a speed of six frames per second, the old Nikon SB-800 had to be left for at least ten minutes to recover.
If you’re lucky enough to own one of the latest high-end, dedicated flash units, chances are it’s equipped with a high-speed sync mode. When used with a compatible camera this mode lets you fire the flashgun at shutter speeds far exceeding the camera’s sync speed. This is extremely useful when you want to use daylight sync for a portrait, but use a large aperture to blur the background.
Repeating or ‘strobe’ flash is another high-end feature that creative users will appreciate. Here the flashgun fires repeatedly during a single exposure to create stroboscopic multiple exposures effects. Strobe flash can make for some astonishing action shots that reveal moments in time too brief for the human eye to register. Attaching coloured gels to your flash window is another great way to extend the creative scope of your flashgun.
It’s so easy
Perhaps the best thing of all about modern camera flash systems is their superb ease of use and accuracy. This is thanks to hyper-intelligent through-the-lens (TTL) flash metering technology, used to calculate the precise flash dosage required for a natural balance between the subject and the ambient lighting.
Basically what happens is that the flashgun fires a series of imperceptible pre-flashes onto the focused subject before the main burst. The camera then measures the illumination reflected back from the subject, calculates the required exposure and communicates the data back to the flashgun – all in a split-second. If the subject’s bright and/or close the flash burst may last just 1/40,000th sec, but with dark and/or distant subjects maximum output – around 1/500 to 1/1,000th sec – may be required.
A flashgun that communicates directly with a camera’s metering system is called a ‘dedicated’ flash. The only downside is that they can be fooled in exactly the same circumstances as your light meter. Predominantly light or dark, backlit or sharply contrasting subjects therefore, will all pose problems for TTL flash systems. You may also wish to alter the metered flash exposure for artistic reasons.
This article shows the quality and variety of techniques that customers benefit from as part of our commercial photography and architectural photography service. Call now to discuss your requirements and timescales on 079101 68536.
Copyright - Adam Coupe Commercial Photography 2008
