Fill-Flash Techniques for Photography
10 Jul 2010
Fill-flash in photography is often misunderstood as there are at least two methods to "fill" flash a photo, balanced-flash and overpowering the sun with flash. But before we breakdown each method, it's important to note the purpose of fill-flash. Besides bringing an image to life, fill-flash is a technique in photography used to brighten deep shadow areas while also adding contrast to the photo—especially when an image is backlit. It's often misconceived that fill-flash is for outdoor use only, not true, you can use it indoors too when a subject has a strong backlight or when ambient light produces low-contrast photos.
Ultimately it's about getting the light right for your subject while keeping your background and sometimes foreground, still interesting, or properly exposed. This is where the life in the image comes in, as I've always stated, light is to a photograph what blood is to our bodies, without it, you have nothing, so think of fill-flash as a blood booster to your subject.
The first step with fill-flash is to ensure that your background and foreground are properly exposed. There is one key rule that can really help your photography and make it an easy process when an outdoor scene is involved or the outdoors is visible (think window in the background) in your indoor photo—the Sunny 16 rule. Basically the Sunny 16 rule states, that on a normal, sunny day, if you set your shutter speed to the equivalent of your ISO (film speed in the old days), then your aperture, or F/stop, will be F/16. There are a few things to take into account, if it's early or late in the day, the sun will be less intense so your aperture becomes a lower value, anywhere from F/4 to F/11, depending on the time of day. And if the outdoors is coming through a window, low-E or double pane windows will reduce this value too.
Here are a few things that can alter the Sunny 16 rule:
1. Time of day. Early in the morning, or late in the afternoon, the light is less intense, so set your camera lens aperture appropriately for the reduced ambient or natural light.
2. If clouds are present, or on an overcast day, open the aperture up at least one F/stop value, normally F/11, during the brightest part of the day.
3. When shooting into a dark background, such as rocks, foliage, building walls, etc., you can open up an full aperture if you need to reduce your depth of field, though your background will be overexposed, but to the viewer, they won't know that, you'll only know the background is lighter than what you originally saw. This is an old photo trick when you can't get enough power out of your flash unit to match the F/16 aperture value. (In other words, you're not shooting into the brightest part of the scene, or into the sky.)
4. When working outdoors with snow, beach, or water, increase the aperture value either one-half or a full F/stop to compensate for the amplified light from these natural reflectors.
So in a nutshell, if you remember that during the brightest part of the day, if your camera is set at ISO 100, your shutter speed at 1/100th, that your aperture value will be at least F/16. That means you'll need a flash output value, to at least balance your image, of a minimum of F/16. While most portable studio flash units can achieve this value, especially those with an output of at least 1000 watt-seconds (make sure it's true, not effective watt-seconds), your light modifier on these units can reduce light intensity—correct this by moving your light source closer to the subject or shooting into a dark background if you cannot achieve the correct output.
For those using on-camera flash, you might have to move in closer to your subject and this could impact the feel of the image as your subject might be distorted with a wide-angle lens. Not to mention, your subject maybe uncomfortable with you breathing down their neck. Think comfort distance between you and your subject.
Avoiding pop-up flash units as they are low-powered in nature and a photographer, as a minimum, should consider investing in a high-powered speedlight or camera flash unit if they cannot afford a portable studio flash system. Having a strong flash output is important, especially if the photographer wants to use the over-power-the-sun technique, though for now, we'll concentrate on balanced, fill-flash.
Balanced fill-flash is just that, a fill of artificial flash (light) onto your subject to bring the subject's exposure value to match that of the background. This helps reduce or eliminate shadows while adding contrast (life) to the image. This method is probably the most popular, mainly because today's flash/camera systems are designed to provide this technique by simply moving camera dials and selecting this exposure method in your LCD screen menu. Sometimes this "auto" technique works (proper exposure), sometimes your subject is too bright (overexposed), while other times the fill-flash isn't noticeable (slightly underexposed). The reasons are because in the "auto" mode, your camera works off sensors and proprietary software programming based on commonalities and averages, this is why shooting in the manual mode and understanding the Sunny 16 rule is best.
Though if you're not into shooting in the manual mode (manual mode is a must for shooting with portable studio strobes), most cameras today have a "flash exposure compensation" dial or menu. This feature comes in handy during those times when the camera's automation is fooled by the scene. In this situation your subject photographs too dark or too light. If your subject is too dark, simply adjust the flash, not camera, compensation by adding (+) 1/3-stop values until you get the correct exposure on your subject, or subtract (-) in 1/3-stop increments if your subject appears too bright or washed out. Check your LCD screen and histogram for proper exposure.
Now it's easy to (balance) fill-flash a subject outdoors, especially if you keep the Sunny 16 rule in mind, however there are times, like a sunset, or indoors, where your background is too dark where you can't achieve this balanced look. Which in essence means you want to capture the ambience of your background while still properly exposing your subject. If you're in manual mode on your digital camera, you'd simply drag the shutter, or slow your shutter speed down—don't worry about a tripod, the duration of the flash is the real shutter speed for your subject. Dropping your shutter speed down will simply brighten your background or allow for proper exposure of the background for effect, while still keeping your subject properly exposed.
Though there are times, especially indoors, where your shutter speed becomes too slow, especially for hand-held photos. The best method to alleviate this problem is to raise your ISO by doubling it each time until you get your background perfectly exposed. Don't worry too much about your subject becoming brighter, as your subject's main light source is the flash, not the ambient light during these types of scenarios, though don't forget to power down your flash unit by the same equivalent. For example, if you doubled your ISO from 100 to 200 or 200 to 400, your camera is now one full aperture value (F/stop) more sensitive to light, so if your flash output measured F/5.6 at the original ISO, you would then bring down your flash output power down by one full F/stop value, or reduce the flash power output by 50-percent from the original setting.
While balanced fill-flash helps brighten up your subject the majority of the time, it will almost certainly add contrast and appear to give your photo some life. However, often your photo takes on the appearance of a cliché "flash" picture. This holds true, especially if your subject has earrings, possibly a hat, or some object around them that is in the flash's path that will cause a hard shadow on your subject. Still other times, if your subject is too close to a background like a wall or tree, then a hard shadow of your subject will fall onto the background. I'm not a fan of "flash" looking photos, especially outdoors, so my preferred method of using fill-flash is the overpowering-the-sun-with-flash technique.
In order to overpower the sun with flash, a photographer must first have a flash system or camera flash that has a substantial power output. For portable studio flash units, ideally 1200 watt-second power packs (true, not effective watt-seconds) with a matching flash head will suffice. One reason for this higher power output is at that the type of light modifier used in front of the flash head will absorb some of that flash energy either through baffles (inside a soft box), diffusion panel (in front of the soft box), reflectors (metal dome reflector on a beauty dish and the pan itself) or in the case with umbrellas, shooting through or bouncing off the fabric.
Rarely will a photographer, especially with female subjects, shoot bare bulb to over power the sun with flash—if so, it's because their subject has a clean, youthful complexion or the terrain has its limitations on where to place the flash. Even with a ring flash, a frosted glass is best and it too will absorb some of the light as the light passes through this diffused glass. Bottom line, don't pay for a portable studio flash system twice, buy one that has the power, though a bit more expensive, you won't regret it later.
The technique for overpowering the sun with flash is based on a photographer's personal taste and style, as some photographers like more dramatic versions of this method, while others just want a tad of the effect. Basically it's all about darkening the background for dramatic impact while keeping the subject properly exposed. Though, the background is overpowered for eye-popping impact of the subject, not necessarily for background elimination or to create a black background. If you want a pure black background, take it to the studio with a black fabric or seamless paper background.
If you recall the Sunny 16 rule, then overpowering the sun-lit background means you need a flash output of at least F/22, one-stop more powerful than the sun when your ISO is equivalent to your digital camera shutter speed. The problem here is that most lenses for today's digital cameras, in the 35mm format, don't go past F/16, though some do, they are usually the higher-end lenses. So if you're lucky, your camera has a higher flash sync-speed than 1/125th of a second—but be careful, some cameras offer this higher flash sync-speed only with their proprietary on-camera flash units and these cameras will not sync at higher speeds (usually above 1/250th) with portable studio flash systems.
If you have this type of camera, which most are manufactured this way, then refer to your owner's manual for the highest studio flash sync-speed. Most cameras today will sync up to 1/200th or 1/250th of a second that works well for most daylight situations to over power the sun by at least one to one and half F/stops than the ambient sunlight (at ISO 100 if you set your shutter speed at 1/200th, you've underexposed the scene by 50% using the Sunny 16 rule on a bright sunny day). Though some photographers prefer overpowering the sun by more than one F/stop, so there are a few things that can be done. One is to use a neutral density filter, such as one that gives you a light reduction of one or two full F/stops.
Neutral density filters reduce the intensity of all wavelengths of light equally, thus no changes in color rendition or hues of the image. The most commonly used neutral density filters are the ND2 (provides for one F/stop reduction) or ND4 (provides for two F/stop reduction) filters. Some photographers even carry an ND8 (three F/stop reduction) or an ND16 (four F/stop reduction). Still other photographers will use a polarizer for at least a one to two F/stop reduction, as polarizers can provide an even more saturated background or sky while reducing or eliminating reflections.
Circular polarizers are specifically designed for use with auto-focus SLR cameras, but they will also work on manual systems without problems. Linear polarizers are used with most video and manual focus photo cameras. They are not recommended for auto-focus SLR cameras. Also, don't use a polarizer if you want reflections in your photos.
Personally, I avoid any filter on my camera lens as my philosophy is simple, a lens is only as good as the last piece of glass in front of it and if I've purchased a $2,000 Canon 85mm F/1.2L USM lens, why would I want to turn it into a $60 filter? Often filters become dirty and scratched and though it's negligible, filters can cause loss of image definition. Yes I own filters, but I use them sparingly. The easiest way to work around using filters, get a powerful flash unit, place it closer to your subject, bring your ISO down to 50 or 100, and raise your shutter speed to the highest sync-speed.
Ultimately how much you want to over power the sun with flash, whether it's a half F/stop or two full F/stops values, is usually the photographer's personal choice. I vary it according to the skin tone of my subject, and sometimes I adjust it according to what my subject might be wearing or the pose itself and the direction of the overhead sun. In fact, whether it's balancing, filling or overpowering with flash, all three will liven up your subject and the latter one will make for more dramatic backgrounds, skies and ultimately a photo with greater impact than a flat, boring image. With digital photography today, photographers have it easy as they can see the results instantly (chimping) and make adjustments on the spot until it suites their photographic style. Now go overpower the sun or fill someone up with flash!