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Flash diffusion


The mini-diffuser is effective and compact
The mini-diffuser is effective and compact

Built-in, camera-mounted and off-camera flash all share lighting problems associated with direct flash that can be solved by diffusing the light. On-camera direct flash provides flat, textureless lighting, while off-camera direct flash creates excessive contrast, with bright light and hard shadow areas.

Diffusion effectively increases the size of the light source. Spreading a flash’s light out over a larger area causes it to “wrap around” a three-dimensional subject. The transition from highlight to shadow becomes more gradual, and the overall effect tends to be a natural, more-pleasing look.

COMPACT CAMERAS

There are several methods of diffusing the light from a flash. Unfortunately, many cannot be used with point-and-shoot and compact cameras that have built-in flash, because the flash itself cannot be swiveled and must always face in the direction the camera is pointed, and because there is so little space between the flash and the lens. Nonetheless, by careful positioning directly in front of the flash, translucent material such as tracing paper or white nylon can be employed to diffuse the flash on such cameras. You must be careful, however, to hold it far enough away that it doesn’t touch the flash, but not too far away that it interferes with the camera, either by blocking the lens, by reflecting light back into the lens, or by blocking the camera’s light meter, focusing or automatic flash sensors. It’s a tricky business, and its softening effects may be minimal since the desired result - a large surface area for the diffuser - is difficult to achieve with such restrictions.


CAMERA-MOUNTED FLASH

Flash units that attach to a camera via a hot shoe, particularly those that have tilt/swivel heads, provide the greatest versatility for on-camera flash diffusion. Here are some of the methods that can be employed:

The mini-diffuser - Various accessories for diffusing the light from flash guns are commercially available. One of our favorites is a small “soft box,” known as a mini-diffuser or “light modifier” that can be purchased from most camera stores. This device is fitted with an elasticized opening that fits over the flash head. (Some have Velcro strips to hold them in place.) The mini-diffuser has folding arms that keep the translucent fabric supported evenly in front of the flash head, and opaque, black sides that prevent stray light from escaping. The mini-diffuser folds flat for storage and can be attached in seconds. Not only will it soften harsh light, but it also eliminates red eye.

You will lose at least two stops with the unit attached, and therefore the aperture for manual flash units must be opened a minimum of two stops from normal - i.e. if the aperture would normally be ƒ/16, use an aperture of ƒ/8 with the mini-diffuser attached. If the flash unit is automatic and sets exposure by reading light reflected back from the subject, the mini-diffuser’s fabric box blocks the flash’s sensor, and therefore the flash cannot be used in automatic mode, but must be set for manual operation. However, if the flash unit has a tilt/swivel head, then the mini-diffuser can be attached to the head if tilted upwards at a 45◦ to 60◦ angle, and the flash’s light sensor will not be blocked. No compensation is needed with TTL camera/flash combinations that automatically adjust for correct flash exposure, but there is still light loss and a therefore a reduction in the flash’s effective range.

Translucent household materials - Tracing paper or other translucent material (including nylon, white parachute cloth or even a section cut from a white plastic milk carton) can be held several inches in front of the flash to produce a relatively-large diffused light. Flammable materials must be kept out of contact with the flash’s lens to prevent their catching fire.

Hankie help - In a pinch, a pocket handkerchief can be wrapped indecorously around the flash head, and held in place with a rubber band. Heat from a repeatedly-fired flash, particularly a powerful unit, may cause the fabric to singe or even burn, and all caution should be used with this technique.

A flah head mini diffuser is fashioned after a much larger studio soft box
A flah head mini diffuser is fashioned after a much larger studio soft box

A hankie over the flash head may not look too slick, but it does diffuse the light. Be careful that it doesn't burn. Flash can get hot.
A hankie over the flash head may not look too slick, but it does diffuse the light. Be careful that it doesn't burn. Flash can get hot.

OFF-CAMERA FLASH

All of the above techniques can be employed with a flash that is mounted to the camera. Removing the flash gun from the camera (see Off-camera flash) opens the door to more diffusion options, for instance, using clamps to hold a flash unit on a light stand so it can be directed at a reflecting umbrella that softens and spreads the light, or through a translucent umbrella, studio soft box, portable diffuser or other diffusion material, providing a similar effect. The flash unit can also be hand-held by either the photographer or an assistant at varying distances behind a large commercial diffuser that is normally used for softening sunlight.

THE DRAWBACK TO FLASH DIFFUSION

The main drawback is a drop in light output. You can lose as much as three stops. The best flash units for diffused light are the powerful ones, providing enough output to shoot at apertures of ƒ/8 or smaller with medium-speed film.

Another drawback is the difficulty in calculating exposure with a manual flash. It can be a trial-and-error process.

Finally, automatic flash units that require light to be reflected back from the subject in order to function properly must be set on manual mode for many of the diffusion techniques.

If your flash/camera system is fully-automatic with TTL sensing, then you will be able to use all of these diffusion methods with the least amount of trouble by allowing your camera to make automatic exposure calculations.




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