Are Two Flashes Better than One?
One of the most common questions relating to flash photography is whether or not your photographs will benefit from using more than one flash. The answer to that, of course, depends entirely on a wide variety of factors, ranging from personal preferences to the type of effect you are attempting to create in your photograph. Below you will find a breakdown of situations where two flashes might be preferred over one single flash, and situations where one flash will typically be more effective.
Using a Single Flash
For the most part, the vast majority of your photographs will not differ appreciably when using multiple flashes. In terms of photo quality, the difference between using one flash or two flashes will not affect your photos to a great degree in most lighting conditions. The main complaint against using a single flash is that this will create images that are considered "flat" in comparison to images created through the use of multiple flashes. While this is true to some degree, most casual photographers will not notice or will not care about the difference in quality created by a single flash when compared to multiple flashes.
The relative benefit, therefore, will generally come from the time and preparation that you will save by using a single built-in or shoe mounted flash. For most lighting situations, then, it would be fair to say that it is generally better from a simplicity standpoint to use a single flash. There are certain situations, however, where multiple flashes will be beneficial, and these will be discussed below.
Using Multiple Flashes
In some instances, you will want to create more interesting composition by adding an additional flash to your artificial lighting setup. Multiple flashes can be mounted together on your camera through the hot shoe or can be positioned externally to the camera itself and triggered remotely through the use of a device known as a flash slave. By positioning lights at angles other than straight at your subject, you can illuminate different areas of your composition, such as the background of your image. This can often create an effect that is more realistic and closely mimics the effects of natural lighting on a subject.
One excellent example of a situation where multiple flashes are often used to create a more realistic and interesting photographic effect is cave photography. When shooting images in a cave or similar setting, you have multiple unique conditions to consider. First, the ambient lighting in the environment will be virtually nonexistent. This means that all of the lighting effects in your image will be created through the artificial light triggered by your camera. A single, straight-on flash will create relatively flat images devoid of shadows, which will appear unrealistic when compared to photographs incorporating multiple flashes. Using two flashes can serve to bounce light off of the roof or sides of a cave to illuminate the cave features from different angles, which creates a more interesting and realistic effect.
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