Fill Flash – Indoors & Out

Flash Techniques:
Fill Flash
I’m surprised at the number of advanced photographers who remain mystified by fill flash.  This powerful technique is simply the blending of two light sources during one exposure.  The primary light source is natural light and the secondary light source is your flash.  During full flash the camera is arbitrarily set at the highest synch speed, but with fill flash, simply shoot in aperture priority and let the flash do the rest.
31165_fillAperture priority is the best mode for using fill flash.  You select the appropriate aperture for the situation and let the camera decide the correct shutter speed.  Assuming the subject isn’t moving and the camera is supported on a tripod, most shutter speeds work.  Your flash can fire at any shutter speed at or below the flash synch speed.  To get started, pretend your flash is turned off and set exposure as you normally do in aperture priority.  Next, set the fill flash to automatically reduce flash output by  -1-1/2 or -2 stops.  Don’t confuse this setup with power settings that manually vary the flash output.  Manual setting will not work as intended.  You want the flash output automatically controlled at your desired setting while in aperture priority mode.  Check your owner’s manual for exact directions for your system.
D6069_fillOnce the flash is set to a substantial minus setting simply shoot as if the flash is not in use.  Fill flash has virtually no effect on the overall exposure.  The magic of fill flash is that it only affects the shadow areas of the image.  Even when set at minus two stops; fill dramatically opens up shadowed areas on cloudy days or during indoor situations.  Shadows can be quite harsh on bright sunny days; consider boosting your fill settings to -1/2 or -1 stop.  My standard setting for indoor/overcast lighting is -2 stops.  Fill light adds a beautiful catch light in the eyes of your subject whether shooting inside or out.  The idea is to blend the flash seamlessly so the subject looks completely natural and not flashed.  Simply reduce the flash exposure to a point well below the natural light exposure and shoot away like normal.  If you’re in doubt about which setting to use, it’s better to err on the side of too little flash.  At least the subject won’t look flashed.
24065_fillUnlike full flash, fill does not freeze subject motion or eliminate camera shake.  Remember, two exposures are taking place, one for the flash and one for the natural light.  If nothing moves, both exposures overlap perfectly as one.  Ghosting occurs if there is movement during the exposure.  Fill light freezes movement the instant the flash discharges, but the subject keeps moving during the time the shutter is open for the ambient light exposure.   The lag time between the flash firing and the shutter closing creates two overlapping images; one blurred and one sharp.  Fill flash won’t freeze the action of your active kids, but it can greatly improve the quality of images inside and out.  As in any normal shooting situation, make sure the shutter speed is adequate for the situation and the let the flash work it’s magic automatically.

Full Flash – Indoors & Out

Full Flash
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.
Grey phase Screech Owl capturing mouse in flight.
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.
F3395.tifMost 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.
Red Knee Tarantula, Brachypelma smithi, MexicoMy 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.

Using Flash – The Basics

The Basics
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.
Special Shutter Speed_basicsFlash 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.
Inverse square law_basicsTo 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.
Bounced on camera flash_basicsThe 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.