For candid photos where indoor light levels are low; flash can save the day. Most interior lighting is quite dim and exhibits a strong color cast. Simply set your camera to the required sync speed and flash quickly eliminates color casts and the quick pulse of light eliminates the need for a tripod, and freedom to react quickly for candid shots. Indoors, flash is capable of freezing movement, such as active children! By definition, full flash means the flash unit provides all the light on a subject. Select the maximum synch speed for your camera and appropriate lens aperture; and the flash automatically supplies the correct amount of light within a given distance range.
The most serious drawback to full flash from a small flash unit is that it’s not flattering and shadows are harsh. Some accessory flash units allow the flash to be aimed up or to the side for bouncing off walls and ceilings. This is a good option for reducing the harshness of direct flash illumination. When using bounce techniques, make sure the wall or ceiling is white to avoid picking up a color cast. Many flash accessories sold to soften the effects of flash have very limited usefulness for anything other than small subjects. They fail to make the light source large enough for a significant improvement.
Whether indoors or out, through-the-lens (TTL) flash metering automatically reads the flash reflected from the subject during the exposure, and turns the flash off when correct exposure is achieved. This system automatically compensates as the flash to subject distance changes. However, no TTL system can fix the exposure difference between widely spaced subjects. Changing the aperture does not bracket exposure in TTL mode. Within a given range, this automatic feature ensures the same amount of light reaches the subject regardless of aperture selected. When you need to lighten or darken the flash exposure, vary flash output via the flash compensation dial and not the lens aperture or shutter speed. Refer to your owner’s manual for precise directions. In practical application, Shutter speed has no effect on exposure with full flash. The shutter just needs to be fully open when the flash is triggered. The extremely short duration of the flash essentially becomes your shutter speed. This is why we can arbitrarily select the fastest flash sync on the camera, since it really is not part of the expose equation.
Most hobbyists readily compensate their natural light exposures for non-average subjects, but seem to forget the need to do the same with automatic flash when illuminating light and dark subjects. Most cameras read flash output the same as natural lighting, so very similar flash compensation is prudent for light and dark subjects. Dial in plus compensation for lighter than average subjects and dial in minus compensation for subjects darker than average. This assumes the subject is large enough in the frame for an accurate reading. If the subject is very small, the flash may read the reflectance of the background causing overexposure, therefore a minus compensation may be required in some situations. Keep an eye on your histogram and adjust the flash compensation as desired.
My primary use of full flash outdoors is to freeze the movement of small active creatures such as butterflies and insects. At close working distances of a few feet or less, and a small aperture, an accessory flash can easily overpower bright sunlight. With full flash as the only light source, natural light is of little concern, and a tripod isn’t needed. The extremely short duration of the flash easily stops moving subjects and eliminates camera shake. It doesn’t get much easier, simply turn on the flash, set the synch speed, pick an appropriate aperture, and your ready to go about shooting handheld.
Small portable flash units have revolutionized 35mm SLR photography, freeing us from the limitations of natural light. Millions of amateurs own cameras with built in flash, yet flash is one of the least understood tools of photography. Understanding just the basics of how flash works, will let you do some pretty amazing things with flash.
Flash photography requires that you learn and work within the quirky characteristics of flash illumination. Light from any single camera mounted flash has two inescapable characteristics. First, light from a small light source is very harsh for portraits. Flattering portraits are usually made with a much larger light source, so don’t expect a small flash to bath your subjects in flattering light. Basic Theory: From ten feet away a single flash unit is a tiny light source when the subject is as large as a person. The same flash unit ten inches from a small insect is a much larger light source. A flash mounted in the camera hot shoe compounds the harshness of a small light source. All built in flashes and even accessory flashes mounted in the camera hot shoe, are too close to the axis of the lens. The lighting is unflattering, often producing red eye where the subjects eyes glow like some alien life form. Moving the flash off camera a few inches can make a noticeable improvement in lighting quality. When using only one flash, I prefer to have it right above the lens, but elevated a few extra inches.
To improve the quality of your indoor flash pictures, try bouncing light off a large white surface. Walls and ceilings work fine as long as they are white. Flash picks up a colorcast when bounced off colored walls and ceilings. Bounced flash is less harsh because the light expands tremendously before reaching the ceiling where the large illuminated area is then reflected downward on the subject, creating an effect similar to that of a much larger light source. Keep in mind that a lot of flash power or distance is lost when light is bounced. Use a wide aperture and stay reasonably close to your subject. TTL flash metering compensates as long as you don’t exceed the flash maximum distance range. Bounce lighting means the light must travel further to reach the subject and power is lost due to light scattering. If your flash is not powerful enough, kick up the cameras ISO a few stops and in effect you have a much more powerful flash.
The second characteristic of all light sources is governed by the laws of physics and is referred to referred to as the Inverse Square Law. This law states that light from any single point light source diminishes according to the square of distance it travels. In simple terms, this means the power of your flash diminishes very quickly with distance. Logically you would think that doubling the distance to your subject would reduce the light reaching that subject by one half. It’s much worse; light reaching the subject is reduced to only one forth. In terms of camera adjustments, you’re loosing 2 F-stops of light when you double the distance. The good news is that your TTL (Through-the-Lens) flash automatically compensates for variations in distance within limits of the flash range. However, no TTL system can correct for light falloff when trying to illuminate subjects near and far in the same shot. In practical terms this means that elements a few feet in front of a correctly exposed subject will be overexposed, and elements a few feet behind will be underexposed. Work around this limitation by keeping subjects at roughly the same distance from the flash. Moving closer to a subject exaggerates light falloff. The best tactic for illuminating subjects at varying distances is to back up. In other words, moving the flash further from the subject reduces the difference in illumination between near and far subjects. With this basic theory, lets move on to full flash and fill flash.