Everything you Need to Know About Camera Flash
Flash is a useful source of artificial light in photography. In early days of photography, when there was no electricity the photographers used powdered magnesium, which they used to burn to produce a ‘flash of light’!
Unless you’re a professional photographer, the chances are good that the camera you’re using – whether film or digital – has a built-in flash. Typically, when shooting indoors, the flash will work adequately if the subject you’re shooting is within ten to twelve feet. Although your built-in flash will permit you to take a photo in a low-light environment, it will not provide the same effect as natural lighting. Rather, pictures taken with an on-camera flash tend to look similar, since the flash produces a flat light that minimizes surface textures.
A flash may be inbuilt in the camera, or separate flashguns may be attached to the camera’s hotshoe. Electronic flash consists of ‘xenon’ filled glass tube. It works on the principle that a sudden discharge of electrical energy through the gas produces an intense flash of light.
The light produced by a flash is harsh, which can cause strong shadows and also makes people to squint. This problem can be reduced by use of a diffuser or with a piece of thin cloth, covering the flashgun.
The duration for which the flash fires, is usually very small. With a manual flash, it may be 1/1000 sec; while with automatic flash units, it may be 1/10,000 sec or even lower. Such short durations can be used to freeze very fast moving subjects, such as a splash of water.
When the ambient light is low, only flash duration is of significance in freezing the action (provided that the shutter speed is correct for flash-synchronization).
Flash power is given by a ‘guide number’ which is the product of aperture and camera to subject distance for correct exposure. For example, if a flash is having a guide number of 32 (in meters), an aperture of f8 will be required, when the camera to subject distance is 4 meters.
Most flashguns incorporate a scale, which gives the value of correct aperture for various distance/ film-speed combinations.
The camera’s shutter should be fully open, when the flash fires. At shutter speeds of about 1/125 sec, the shutter begin to close even before the flash has fired, thus exposing only a part of the frame. In order that the frame is properly exposed, the shutter speed should not be (typically) higher than 1/125 second, when using flash. This is called ‘flash synchronization’ speed.
Flash synchronization speed is normally indicated in red color, on the shutter speed dial.
Inverse Square Law
For a point light source, the intensity of light is inversely proportional to the square of the distance between the light-source and the subject. This is known as the ‘inverse square law’- It means that, an object, which is at double the distance, will receive only one-fourth the light’.
When using flash, it should be ensured that all the subjects are approximately at the same distance from the flash.
You will need to experiment a bit to see what your digicam’s flash can and cannot do. Most built-in flash units are small and are designed to light up subject close by. If you’re in a situation where you’re shooting a large area, such as at a sporting arena, the flash can’t possibly illuminate the whole scene. If you try to shoot the entire stadium, you’re likely to end up with an underexposed photo.
Some more expensive models have stronger flashes that work at longer distances. Or they may have a hot shoe, a mounting device that enables the addition of a flash unit.
Try out your flash in several different situations. Take a series of indoor shots with your subject standing or sitting at different distances horn your camera. Take shots of your subject in front of a light source, such as a window, with and without the flash to see how a flash can “fill” in darkened areas.
Some cameras allow you to adjust your flash unit to one of the following modes:
The camera gauges the available light and fires the flash if needed. In certain situations, the resulting image can be well lit, but the background may be almost black. Some high-end cameras avoid the problem of silhouettes by firing the flash if they detect a backlit situation.
Because every flash has a useful range, the effects of the auto flash will depend on how bright a light it produces and how far the light has to travel. Flash light becomes dimmer the farther it has to travel. The further away the subject is from the camera, the less light will be reflected to the camera. Objects closer to the camera will appear lighter than objects in the background.
When you are taking a photo of a scene with multiple subjects at different distances from the camera, the exposure cannot be correct for all of the subjects. Usually those closest to the camera will be properly exposed. The farther the subjects are from the camera, the darker they will appear in the picture.
When shooting in bright daylight, the sunlight may cause dark shadows in certain areas (e.g. under the subject’s eyes). In such conditions, the flash may be used to brighten up the dark areas. This is called ‘fill flash’.
The fill flash mode allows you to add light to an image without affecting the exposure settings. A photographer will turn on the fill flash mode when he wants to add light to the backlit (shadowed) areas in the scene he is shooting. For instance, if a subject is standing in front of a large window, turning on the fill flash will help illuminate the subject’s face so that he or she does not look like a dark shadow. A photographer can also use fill flash in normal sunlight when he or she wants to fill in the shadows on the subject.
Generally, the flash exposure for fill-in flash is kept one-half than that required for exposure solely by flash. (It means that aperture is kept at one stop less).
Night flash, or night portrait mode, combines a flash exposure with a longer capture speed. This mode is ideal for shooting room lights or an evening sky with a brightly lit subject. If your camera does not have night flash, the next best thing is to use fill flash, although the results will not be quite as good. Another option is to take separate pictures of the foreground and the background and blend them using editing software.
When inbuilt flash is used, or flash is mounted directly over the camera, it causes the light to reflect from the retina of subject’s eyes, causing the problem of ‘Red eye’. This problem can be eliminated by using the flash to one side of the camera, using a flash-synchronization cable.
Some cameras also have a red-eye reduction feature, in which a series of small flashes fire, before the actual flash. This causes the iris to contract, thus reducing the problem of red eye.
This mode helps to reduce the “red eye” effect that occurs when a flash is reflected in the subject’s eyes. Red-eye reduction works by low-power flash, or burst of flashes, just before the primary flash is fired. The low light causes the iris of the eye to close slightly, diminishing chance of the flash being reflected there.
There are five ways to combat red eye in pictures:
- Move the external flash farther away from the camera lens.
- Tell the subject not to look directly at the camera.
- Increase the overall lighting in the area where the picture is being taken.
- Use the red-eye reduction mode on your camera.
- Use image-editing software to remove red eye.
If the flash is used at low shutter speeds (slower than that required for flash synchronization) it is called a slow-sync flash. In such a case, the main subject is exposed by flash as-well-as ambient light, while the background is exposed by ambient light only. If the subject is moving, its path of movement will be recorded as blurred.
Some cameras offer a slow-sync flash, which increases the exposure time beyond the normal flash. This mode helps illuminate background shadows that normal flash mode misses. The slow synchronized mode works by allowing the shutter to remain open longer than normal so that the background appears lighter.
Sometimes when using slow sync, fast moving objects or a shaky camera will cause images to blur. To avoid blurring in your photo, use a tripod and/or photograph stationary objects. If you want to make lemonade from lemons, use blur creatively for interesting effects. For instance, using slow sync to photograph moving cars can create blurry trails in the resulting image, conveying a sense of speed in the photo.
Some camera have features like front curtain sync, or rear curtain sync, which means that the flash will fire at the beginning or at the end of exposure, respectively.
This mode lets you use a separate flash unit similar to ones used with 35mm SLR cameras. In this mode, the camera’s built-in flash is turned off and you must manually set the correct exposure to work with the flash.
Additional Light Sources
Hot spots and red eyes are some of the problems that can arise when shooting with a flash. If your camera works with auxiliary flash units, you can move the flash away from your subject, which will help reduce these problems. However, if your digicam does not accept an auxiliary flash, your best may be to turn off the flash and use another source of light.
Your digital camera may be designed with a built-in flash and no connection for an additional flash unit. You can still get the benefits of an external flash by using a device known as a slave unit.
A slave unit is a small battery-operated flash unit with built-in photo-eyes. The slave unit fires a flash when it senses another flash of light. There are some slave units that are designed specifically for use with a digital camera. If you’re taking photos at your brother’s wedding reception and the room is dimly lit, you can sprinkle slave units throughout the space.
Then, when you take a picture, all the slave units will go off time, allowing you to get a great shot in the well-lit room.
In studio photography, two or more flash units may be required to be used for providing main, fill-in and background lights. All the flash units must fire in synchronization. This can be achieved by use of slave units, which are built into flash-heads, or separate slave units may be used.
A slave unit contains a photoelectric cell, which senses the light from main flash and fires other flashguns, in synchronization.
If you already own studio lights for use with your film will come in handy with your digicam. If not, you may decide to purchase some inexpensive photoflood lights, the same kinds that are used with video camcorders.
Another option is to use what you already have at home. Look around the house for creative solutions. Placing a subject near a window may provide enough light to do the trick. Turn on small table lamps or purchase clip-on lights at the hardware store for extra lighting. Or create a backdrop using a white sheet or board and-voila! -you’ve created your own mini photography studio.
Getting the Correct Exposure
Controlling the amount of light that hits the CCD in your digital camera is one of the necessary components of capturing an image successfully-and it is one of your biggest challenges as a digital photographer. Too much or too little spoils your final image, rendering it too light or too dark. Having certain tips and tools at your disposal, along with lots of practice will allow you to wrestle with the unpredictability of light and come up a winner.
Photographers use gray cards, available in camera stores, to help get correct exposures. Place the gray card in front of the subject so that it is in the same light as the subject. Move in close to the card so that all you see in the viewfinder is the gray card.
Conventional film cameras use film of different speeds, or ISO ratings. In a similar way, CCDs in digital cameras have ISO ratings that indicate their sensitivity to light. The higher the ISO rating, the less light is needed for full exposure. For instance, a CCD with an ISO rating of 400 needs less light to achieve full exposure than a CCD with an ISO rating of 100.
If your digicam allows you to change the sensitivity of the CCD from one shot to the next, you can adjust the ISO setting as the lighting dictates. For instance, in a low-light situation you can increase the ISO setting to get as much light as possible striking the CCD.
When you are photographing a subject with a bright area behind him that is casting him in shadow, you’re encountering the challenge of backlighting. Most folks know that when shooting outside on a sunny day the sun should always be behind the photographer. But sometimes it is simply not possible for you to set up the shot this way.
A problem arises when backlighting occurs because the camera’s light meter reads the scene as being overly bright and shuts down the aperture to compensate. The end result is a photograph that is underexposed.
What’s the solution? First, if your camera has an exposure override, you can easily correct the problem by opening up the aperture or slowing down the shutter. By giving your subject a few more stops of light, your image will come out looking good.
You cannot always avoid backlighting, but there are ways to take a great photo anyway, even if you can’t move the sun or other source of light. Here are some tips to keep in mind:
- Start with the rule we all learned with our first cameras: Position your subject so that the sun is behind you, not him.
- Let the subject stand where he is but move yourself so that the sun is behind you.
- Turn on your flash. Your camera may refer to this mode as fill flash mode as it allows you to use your flash in any light condition.
Shooting at Night
Taking photographs at night is easier today thanks to digital cameras and a few good accessories. Because you can preview your shot using the LCD screen on your digital camera, you can be quite certain of what your exposure should be. When shooting at night, be sure to use a tripod to hold the camera steady and a cable release or self-timer. Experiment with different shutter speeds.