|1. Fill Light
One of the primary uses of flash or a small LED is to introduce fill light to balance exposure and light your subject. Fill light is useful when your main subject is darker relative to its surroundings or you want to give your main subject more emphasis. For this image, the field was lit by gorgeous morning light, but unfortunately, the cheetah was standing in the shadows. I used flash to create fill light to balance the exposure and to add catchlights to the cheetah's eyes. I reduced the flash's power setting, as I didn't want to make the cheetah too bright, resulting in an artificial look—instead, I wanted the fill light to blend in with the rest of the scene. Nxai Pan National Park, Botswana. Canon EOS 70D, Canon EF 200-400mm ƒ/4L IS USM with internal 1.4x extender, ƒ/5.6, 1⁄200 sec., ISO 400
As a nature photographer, too often you're at the mercy of existing natural light. Wouldn't it be great if you could carry a small sun with you to direct light where and when you wish? Well, to some extent, you can, with an LED or a flash—a vital, although often ignored, nature photography accessory, particularly for wildlife photography.
Flash has multiple uses: It can be used at low power to add an attractive catchlight to a wildlife subject's eyes; it can provide fill light for a subject in shadow; and it can be used creatively in low light to produce surreal images. It can add punch to subjects in flat light, revealing colors. It can be used to photograph subjects in low light, and to freeze the action of fast-moving subjects, such as a flying hummingbird. I'm always thinking of ways to creatively experiment with flash, and I encourage every nature photographer to do the same.
I should note at the outset that by "flash" I don't mean the pop-up flashes that are commonly found on many DSLR cameras, which don't have sufficient power for most critical uses. If you really want to get serious about flash photography, I recommend a good off-camera flash, preferably one with a lot of power. Flashes with higher guide numbers (a measure of the flash's output) have more range, expanding the reach of your flash and its potential for creative use.
2. Creative Use Of Flash
You can also use flash in a more creative fashion, such as mixing long-exposure blur with stopped action. For this image of snow geese in flight during early-morning twilight, I used flash to freeze the motion of the birds, setting the camera exposure to record the low ambient light. The result is a "ghostly" look, as if two separate exposures had been combined. Bosque del Apache National Wildlife Refuge, New Mexico. Canon EOS 5D Mark III, Canon EF 16-35mm ƒ/2.8L II USM, ƒ/5.6, 1⁄15 sec., ISO 400
Flash Shooting Modes
Through-the-lens mode (E-TTL for Canon users, i-TTL for Nikon users) is the most useful mode for flash photography for most uses. This allows sensors in the camera to automatically adjust the amount of flash output, taking into account subject distance and your camera and flash exposure compensation settings. Manual mode may be preferable in specific situations, usually when conditions are very controlled, such as at a bird feeder, where the distance between the flash and the subject doesn't significantly change. In manual mode, you'll have to manually set the flash power to the desired level.
I love shooting in backlighting, especially at sunrise and sunset. Sometimes, I find that just a hint of fill light can greatly benefit subjects shot in backlight situations. For this photo of a springbok, the sunset backlighting was absolutely stunning. I dialed back the flash compensation, adding just a hint of fill-flash to prevent the subject from being rendered in silhouette and to add catchlights to the eyes. Etosha National Park, Namibia. Canon EOS 70D, Canon EF 200-400mm ƒ/4L IS USM with internal 1.4x extender, ƒ/8, 1⁄250 sec., ISO 400
When shooting flash, it's important to learn how to use flash compensation, which allows you to control flash output levels. When used improperly, flash can look artificial; flash compensation can help you avoid an "over-flashed" look, with natural and pleasing results instead. Flash compensation is actually quite easy to use, as it works very similarly to exposure compensation on your camera. It's measured in stops (generally, 1⁄3-stop increments), and you can dial in extra flash exposure (+ stops) or less (- stops). Almost always, I end up reducing flash output by dialing flash compensation to a negative number, often going as low as -2 or -3 stops. This helps keep the flash illumination from looking artificial, as at reduced power, light from the flash mixes with the ambient light for a more natural result. For most uses, your aim will be to use flash to add just a hint of additional light so the result is complementary to the natural light and not overpowering. There's no easy rule of thumb, as the amount of flash compensation you require will depend on ambient light conditions, your subject, and the distance between your subject and flash. Try starting at -2 stops, and experiment from there until you find the perfect amount of fill light.
4. Soften Hard Shadows
When working in harsh light, adding some fill can soften shadows, allowing for a more pleasing image. With this male lion resting to escape the heat of the day, the lion was partially in the shade, with dark shadows falling unevenly across his face. I used flash at low power to add some fill light to the shadows, balancing the exposure. Notice that I didn't eliminate the shadows entirely; I wanted to keep a hint of the shadows to add some interest to the shot.Central Kalahari Game Reserve, Botswana. Canon EOS 5D Mark III, Canon EF 200-400mm ƒ/4L IS USM with internal 1.4x extender, ƒ/5.6, 1⁄160 sec., ISO 100
It's important to note that most camera systems won't let you use shutter speeds higher than 1⁄200 or 1⁄250 sec. when working with flash, unless you enable high-speed sync mode (HSS for Canon, Auto FP for Nikon). Basically, high-speed sync works by firing the flash longer than it does in standard flash mode, which, unfortunately, reduces the maximum output of your flash and thus can limit your ability to illuminate more distant subjects.
Light can also be used to add an attractive catchlight to your subject's eyes, adding life and sparkle to the eyes. For this image of a white-headed capuchin monkey, I used my flash at low power to balance the exposure between the shadowed monkey and the brighter background, placing more visual emphasis on my subject and adding catchlights. Osa Peninsula, Costa Rica. Canon EOS 5D Mark III, Canon EF 200-400mm ƒ/4L IS USM with internal 1.4x extender, ƒ/5.6, 1⁄200 sec., ISO 3200
Another consideration is curtain sync. The shutter on your DSLR has both a front curtain (which starts the exposure) and a rear curtain (which ends it). By default, your flash is set to fire when the front curtain opens (this is known as front curtain sync). Front curtain sync will work fine for the vast majority of your flash uses, but you have the option of setting your flash to rear curtain sync, which fires the flash right before the rear curtain closes at the end of the exposure. With longer exposures, you can achieve creative motion-blur effects with moving subjects, using the ambient exposure to blur the motion and flash to stop the action. Rear curtain sync ensures that any motion blur shows up behind the moving subject, rather than in front.
6. Using Flash As The Main Source Of Light
In certain circumstances, you may wish to use flash as the main source of light, such as when shooting at night, when you won't have any ambient light to mix with the flash. For example, I came across this tent-making bat underneath a palm leaf during a night walk. With no ambient light, I used my flash as the primary light source. Osa Peninsula, Costa Rica. Canon EOS 5D Mark III, Canon EF 70-200mm ƒ/2.8L IS II USM, ƒ/22, 1⁄125 sec., ISO 100
A bracket is probably your most useful flash accessory. Raising or moving the light off-camera helps avoid an artificial red-eye look in your photos (though, in most animals, the color is different than with people), which results from the flash bouncing light directly off the animal's eye back to the lens. A bracket changes the angle of the light relative to the lens, reducing or eliminating the red-eye effect. If using a bracket, you'll need an off-camera shoe cord to connect your flash and camera and retain TTL control. LED or other continuous lights don't need a tether.
7. Bringing Out Color
A hint of fill light can work wonders when shooting in flat lighting situations. Fill helps reveal color and contrast. For example, with this image of a buff-tailed coronet, I used flash at low power to balance the light between the sunlit leaves in the background and my main subject, which was in flat shadow light. The flash reveals the bird's brilliant colors, similar to how the bird would have looked in bright sunlight. Andes Mountains, Ecuador. Canon EOS 5D Mark III, Canon EF 200-400mm ƒ/4L IS USM with internal 1.4x extender, ƒ/8, 1⁄15 sec., ISO 400
Another useful accessory is an extender, which works by mounting a Fresnel lens in front of the light, focusing the beam of light and allowing it to travel farther. This is helpful when photographing distant wildlife subjects or in situations where you need a narrow beam of light to selectively light your subject. Other accessories are designed to soften and diffuse the light coming from your flash, such as softboxes and diffusers. These are particularly useful when photographing intimate and macro subjects, where the harsh light of an un-softened flash may be undesirable. Colored filters and gels are also available if you want to change the color temperature of the flash light (which is a neutral light similar to middle-of-the-day daylight). Warming filters may be especially useful when trying to balance fill light with the colorful light of sunrise or sunset.
Finally, an external flash battery pack is useful when shooting rapid bursts of images. Battery packs recycle much quicker than the internal flash battery unit, and also allow you to shoot flash for longer without having to switch batteries.