The art and technology of photography can be overwhelming to the facial plastic surgeon. Photographic documentation of patients undergoing rhinoplasty is essential for patient consultation, perioperative planning, and postsurgical evaluation. Possession of a basic understanding of photographic principles, technique, equipment, as well as consideration regarding consistency of patient positioning is essential for producing the best photographic results. This article reviews the basic principles of photography and discusses their application to facial plastic surgery practice, and rhinoplasty in particular.
The art and technology of photography can be overwhelming to the facial plastic surgeon. A basic understanding and appreciation of this vital tool is invaluable in surgical practice, especially in rhinoplasty. Photographic documentation of patients undergoing rhinoplasty is essential for patient consultation, perioperative planning, and postsurgical evaluation. Developing a technique to ensure standardized, high-quality images requires an understanding of the basic principles of photography as well as an understanding of the equipment used, proper lighting, and patient positioning. This article reviews the basic principles of photography and discusses their application to facial plastic surgery practice, and rhinoplasty in particular.
Equipment/camera
With the advent of the digital single-lens reflex (SLR) photography, 35-mm film SLR cameras are no longer the gold standard. Digital cameras offer many new advantages, such as instantaneous pictures, ability to crop and adjust on a computer, and images that can be easily stored and filed. Although point-and-shoot cameras are less expensive, the resolution of these models is lesser than the digital SLR cameras. Digital SLR cameras also afford the ability to change lenses and adjust settings that control aperture size, shutter speed, and exposure. An understanding of the correct manipulation and use of these settings is critical to obtain consistent, high-quality images.
Focus/focal Point
The goal of photography in rhinoplasty is to attain sharp, clear images, which emphasize the fine details of nasal anatomy. Depth of field (DOF) in a photograph is the distance range in which all included portions of an image are in sharp focus. The DOF should be sufficient to allow focus of the entire face, and the focal point, which is the point in the photograph that appears to be the sharpest, should be the nose. Digital SLR cameras allow the photographer to change the DOF through manipulation of the focal length of the lens, distance from photographer to subject, and aperture size. These 3 factors are critical to get the best DOF for photographing patients undergoing rhinoplasty.
The DOF varies inversely with the focal length of the lens used. Point-and-shoot cameras have lenses with short focal lengths that help to keep everything in focus (large DOF). Digital SLR cameras allow for interchanging lenses with different focal lengths. However, as discussed later in this article, distortion can occur with change of focal lengths. Thus, changing focal length to optimize DOF is less than ideal in facial plastic surgery.
The DOF varies directly with the distance between the photographer and the subject. Objects that are photographed at long distances will be seen with greater DOF for any given aperture or focal length of the lens. Given the space constraints, the distance between the photographer and the subject cannot be easily manipulated to increase DOF in the photography studio.
Controlling the aperture size is the best way to increase the DOF because aperture size can be manipulated without the distorting effects of changing focal length and the manipulation does not require a large room. The aperture size varies inversely with the DOF. Thus, a camera with an infinitely small aperture size would have an infinite DOF. This is most closely demonstrated in pinhole film cameras, which have a near-infinite DOF. Aperture size is measured in f-stops, the value for which is a calculation based on the ratio of the focal length of the lens to aperture diameter in millimeters. An f-stop of f/2 is therefore a much larger aperture size than an f-stop of f/8. An f-stop of f/8 provides greater DOF than an f-stop of f/2. This can be appreciated in Table 1 , which gives the corresponding aperture area for different f-stops of a 50-mm lens; with each stepwise increase in f-stop, the aperture area is roughly halved. The effect of aperture size on DOF is illustrated in Fig. 1 . In this figure, the DOF increases dramatically as the f-stop is increased from f/2.8 to f/32.
| F-stop | Aperture Size (mm) (50 mm/f-stop) | Aperture Radius (mm) (Diameter/2) | Aperture Area (mm 2 ) |
|---|---|---|---|
| f/1 | 50 | 25 | 1963 |
| f/1.4 | 35.7 | 17.9 | 1002 |
| f/2.0 | 25 | 12.5 | 491 |
| f/2.8 | 17.9 | 8.9 | 250 |
| f/4 | 12.5 | 6.3 | 123 |
| f/5.6 | 8.9 | 4.5 | 63 |
| f/8 | 6.3 | 3.1 | 31 |
| f/11 | 4.5 | 2.3 | 16 |
| f/16 | 3.1 | 1.6 | 8 |
| f/22 | 2.3 | 1.1 | 4 |
While attempting to improve DOF by changing aperture size, it is important to realize that changing the aperture size will affect the exposure. Increasing the f-stop, and thus increasing DOF, results in less light entering the camera. Two factors may be manipulated to maintain proper photographic exposure when the f-stop is increased. The first factor is the sensitivity of the medium used to light. In film cameras, this was measured with the American Standards Association (ASA) or International Organization for Standardization (ISO) scale. The higher the ISO the greater the sensitivity of the medium to light. Digital SLRs have the capability to change the ISO value. The effect of decreasing the aperture size can also be counter-balanced by decreasing the shutter speed to prevent underexposure. Typical shutter speeds include a range from 1/60 to 1/1000 of a second. Therefore, if an increase in the DOF is achieved by increasing the f-stop, it is important to decrease the shutter speed as well.
Although these settings can be completed manually, most digital SLR cameras now have multiple modes that take the guessing out of determining the correct shutter speed for a particular aperture size for each lens. These automated options include the aperture priority mode (A mode), in which setting the photographer manually adjusts the aperture size and the camera adjusts the remaining settings, and the shutter priority mode (S mode), in which the photographer controls shutter speed and the camera automatically adjusts the rest. There is also a programmed mode, in which the camera automatically adjusts all of the settings. It is the author’s experience that using the aperture priority mode will ensure the best DOF, while the camera adjusts other parameters to ensure optimal exposure.
Lenses
Although one of the advantages of using an SLR camera is the choice of a wide variety of lenses, it is crucial to understand the importance of the focal length of the lens. The focal length of a lens is defined as the distance in millimeters from the optical center of the lens to the focal point, which is located on the sensor or film if the subject is in focus. The camera lens projects a part of the scene onto the film or the sensor. The field of view (FOV) is determined by the angle of view from the lens out to the scene and can be measured horizontally or vertically. Larger sensors or films have wider FOVs and can capture more of the scene. The FOV that is associated with a focal length is usually based on 35-mm film photography. In 35-mm photography, lenses with a focal length of 50 mm are called normal because they work without reduction or magnification. Wide-angle lenses (short focal length) capture more because they have a wider picture angle, whereas telephoto lenses (long focal length) have a narrower picture angle.
Digital cameras, of course, do not use 35-mm film, but images are captured on sensors called charged coupled devices (CCDs). These CCDs are smaller than 35-mm camera frames. As a consequence, the smaller sensor of the CCD captures only the middle portion of the information projected by the lens compared with the 35-mm film frame area, resulting in a cropped FOV. This is the same effect as having a lens with a longer focal length. Similarly, an equivalent 35-mm film camera would require a lens with a longer focal length to achieve the same FOV ( Fig. 2 ). The effective lengthening of focal length is termed the focal length multiplier (FLM) and is used to correct the difference in size of the sensor to the traditional 35-mm window. The FLM is equal to the diagonal of 35-mm film (43.3 mm) divided by the diagonal of the sensor. For example, for Nikon digital SLR cameras (Nikon Corp, Tokyo, Japan) the FLM is 1.5. Therefore a lens with a focal length of 60 mm would be equivalent to a 90-mm SLR lens when fitted on a digital Nikon SLR. By convention, the focal lengths on lenses are listed as calculated for a 35-mm film camera.
