Although it was originally utilized for medical documentation, the ring flash is now commonly associated with specific types of photography. Ring flashes are at once revered and reviled among photographers due to the distinct lighting effect that it leaves on pictures.
A ring flash is a circular, external flash that affixes to the end of the lens on a dSLR. The ring contains several flash components that simultaneously emit light when a picture is taken. Since the flash creates light from multiple points of origin, ring flashes eliminate virtually all shadows in pictures. The placement and effect of the ring flash makes them a coveted item among photographers who specialize in macro, or close-up, photography. Using the traditional mounted flash for macro photography is not feasible due to how close a photographer must get to their subject in order to take the picture. When used in close-up portraits, mounted flashes create a shadow on the subject because there is not enough distance between the flash and the subject; the lens actually ends up obstructing the flash. With a ring flash, the source of light is moved from the top of the camera to directly in front of the subject so as to eliminate any shadows created by the flash's burst of light
The effects that ring flashes create in a photograph have resulted in this accessory being closely associated with fashion and portrait photography. If you've ever seen a portrait of a model or celebrity in a magazine and noticed glowing halos in their eyes, that is the result of a ring flash. Some photographers love the halo-look in eyes, some photographers hate the look, which means this particular flash may not be for everybody. At best, it shouldn't be considered a necessary piece of equipment but, rather, a creative accessory.
The biggest drawback to ring flashes actually has nothing to do with their effect but rather their cost. A true ring flash will probably start at around $500, which is an incredible expense for equipment you probably won't be using regularly. Fortunately, cheaper alternatives are available for photographers who want to experiment with a ring flash. Ring flash adapters, which are considerably cheaper, are attachments that connect to your mounted flash and funnel the light from the flash out through a ring encircling the lens. Furthermore, some innovative photographers have designed makeshift ring flash adapters using common household items.