Cosmetic dentistry beauty & science

22 I I special _ digital photography the lens barrel, the lens magnification ratio is closer to 1:15 for portrait photography; 1:3 for dental views, including normal smile and re- tractedviews,aswellasocclusalviews;and1:1.5 for dental views, including close-up retracted views. Please note that these ratios can vary with sensor (with full-frame sensor) and patient face size. Selecting the correct settings is easy be- cause the ratios are etched or printed on the barrel of the lens (Fig. 1), and there are only three sets to think about and to switch between during the shots.2 _Lighting system Many practitioners choose a ring flash for ease of use. A ring flash creates a uniform burst of light, useful for taking pictures of posterior teeth, areas of difficult access and intra-oral im- ages using mirrors. Camera-mounted electronic flashes are available in numerous shapes and sizes. The best way to choose a flash is to visit a dental retail showroom (Figs. 2 & 3). _Technical jargon Aperture or f/stop: This important setting controls the amount (intensity) of light striking thesensor.Itisactuallyanadjustablehole(aper- ture) in the lens through which the light passes (Fig. 4). The aperture size is calibrated in f-stops and numbered from about f/2.8 to f/32 for most DSLR cameras; the larger the number, the smaller the lens opening. The f-stop affects the depth of field. Depth of field: This determines which parts of an image are in sharp focus. Cameras are unable to focus on everything simultaneously, unlike thehumaneye.Thedepthoffielddeterminesthe extent of focus in front of and behind the plane of critical focus. Furthermore, the depth of field for close-up photography is usually small (a few millimetres) and hence the point of focus is crucial for ob- taining sharp images. The depth of field varies inversely with the aperture opening. A wide- open lens with an aperture of f/8 has little depth of field, but if stopped down to f/22 almost everything from front to back will be sharply focused (Fig. 5).5 White balance: This setting adjusts the cam- era so that colours in the image look natural.2 You will want to set your camera’s white balance for flash illumination from standard to neutral. _Settings for optimum exposure Achieving correct exposure is a quintessen- tial requirement of photography.5 Exposure is the process of recording light on the digital sen- sor. The amount (intensity) of light is controlled by the aperture setting, while the sensor’s sensi- tivity is controlled by adjusting the ISO number (discussed below). More specifically, exposure is the amount of light that strikes the sensor over a specific period.2 Time is controlled by the shutter speed, measured in fractions of a second. Most contemporary cameras have automatic exposure, which calculates the shutter speed once the aperture has been set (in aperture priority mode metering, printed Av; Fig. 6). How- ever, with dental photography one aspect in Fig. 5_A wide-open lens with an aperture of f/8 has little depth of field, but if stopped down to f/22 almost everything from front to back will be sharply focused. Fig. 6_Most contemporary cameras have automatic exposure setting. cosmeticdentistry 3_2013 Fig. 5 Fig. 6