Digital dental photography. IN BRIEF • Since most camera and equipment set- ups for dental photography are identical, PRACTICE the steps outlined in this article need Part 6: camera settings only be performed once. • The main camera settings relate to depth I. Ahmad1 of fi eld, exposure and white balance calibration. • Spending a little time at the beginning VERIFIABLE CPD PAPER making the necessary setting will avoid frustration, and pay dividends in the long-term. Once the appropriate camera and equipment have been purchased, the next considerations involve setting up and calibrat- ing the equipment. This article provides details regarding depth of fi eld, exposure, colour spaces and white balance calibra- tion, concluding with a synopsis of camera settings for a standard dental set-up. Having chosen a camera, lens, lighting and of and behind the plane of critical focus. accessories, the next step in preparation The plane of critical focus is the point to for taking a photograph is setting up and which the lens is focused. For portraiture, calibrating the equipment. Since most of the depth of fi eld is usually divided into dental photography uses similar set-ups, one-third in front and two-thirds behind the settings and calibrations need only to the point of focus, but for close-up pho- be performed once. The main items to con- tography the division is equal, ie one-half sider are depth of fi eld, exposure, colour in front and one-half behind. Furthermore, spaces and white balance calibration. the depth of fi eld for close-up photogra- phy is usually small (a few millimetres) Fig. 1 Small depth of fi eld: a wide aperture DEPTH OF FIELD opening will result in only a few items being and hence the point of focus is crucial for sharply focused, for example the red bead in Depth of fi eld determines which parts of obtaining sharp images. the centre an image are in sharp focus. Unlike the Most digital SLRs (DSLRs) have the human eye where everything is in focus, capability to set auto or manual focusing. cameras do not share this luxury. Depth of For the majority of situations auto-focus fi eld determines the extent of focus in front works well, but the dental environment of bright teeth surrounded by pink gingivae FUNDAMENTALS OF DIGITAL with a dark oral cavity sometimes causes DENTAL PHOTOGRAPHY malfunction of the focusing mechanism. If pictures are constantly out of focus, 1. Digital dental photography: an overview switching to manual focusing is a solution. 2. Purposes and uses Some high-end digital cameras can display 3. Principles of digital photography a live video image of the subject being Fig. 2 Large depth of fi eld: a small aperture 4. Choosing a camera and accessories opening will result in many items being photographed, either via a monitor on the 5. Lighting sharply focused (compare with Fig. 1) back of the camera or on a computer lap- 6. Camera settings top screen via a USB or Firewire cable. 7. Extra-oral set-ups The advantage is that focusing, framing, the patient may have moved before the 8. Intra-oral set-ups composition and exposure can be checked camera has updated the live image. 9. Post-image capture processing with a preview shot before the fi nal picture Depth of fi eld varies inversely with the 10. Printing, publishing and presentations is taken. Furthermore, with magnifi cation, aperture opening. A wide-open lens with focusing is possible by viewing individual an aperture of f4 has little depth of fi eld 1General Dental Practitioner, The Ridgeway Dental pixels. This facility is ideal for still life whereas if stopped down to f22, almost Surgery, 173 The Ridgeway, North Harrow, photography but of limited use in dental everything from front to back will be Middlesex, HA2 7DF Correspondence to: Irfan Ahmad photography. The live image is constantly sharply focused (Figs 1-2). As close-up Email: [email protected] refreshed to compensate for camera and dental photography has a small depth of www.IrfanAhmedTRDS.co.uk subject movement and is not a true repre- fi eld, it becomes essential to have a small Refereed Paper sentation in time of what is being viewed. aperture opening, say f22, so that as many Accepted 15 November 2008 DOI: 10.1038/sj.bdj.2009.607 For example, teeth may appear sharp on teeth as possible or a large area of soft ©British Dental Journal 2009; 207: 63-69 the screen, but when the picture is taken tissue is in focus. In theory, to obtain a BRITISH DENTAL JOURNAL VOLUME 207 NO. 2 JUL 25 2009 63 © 2009 Macmillan Publishers Limited. All rights reserved. PRACTICE Fig. 5 When using electronic fl ash, the Fig. 3 The aperture on a macro lens should shutter speed must be set to synchronise not be set smaller than f22 to prevent Fig. 4 The shutter speed should be fast with the fl ash output, represented by a diffraction enough to prevent blurring ‘lightning’ symbol greater depth of fi eld one could consider The scale for the brightest using even smaller apertures, say f32 or exposure (plus) is further apart f64, but this practice deteriorates the image quality due to diffraction. When light rays are bent around edges of objects they pro- duce an iridescent or rainbow-like effect termed diffraction. This is more evident the smaller the aperture diaphragm, resulting in decreased resolution. Therefore, set- ting the aperture to smaller than f22 will seriously diminish image clarity without a substantial gain in depth of fi eld. This is the reason why most macro lenses are designed with diaphragms that do not The scale for the darkest close smaller than f22 (Fig. 3). exposure (minus) is closer together EXPOSURE Fig. 6 A histogram with a logarithmic scale from the darkest (minus) to the brightest (plus) exposure Achieving correct exposure is a quin- tessential requirement of photography, the consequences of which are blatantly factor is ensuring that the shutter speed by a ‘lightning’ symbol (Fig. 5). obvious. Exposure is a combination of is fast enough to prevent image blurring With analogue photography, automatic two camera settings, the lens aperture and due to patient movements or camera shake exposure with electronic fl ashes was rela- the shutter speed. Exposure explains how (if not tripod mounted) – see Figure 4. A tively simple. The TTL (through the lens) light acts on a photosensitive material, for fast shutter speed (minimum 1/125 s) is metering and OTF (off the fi lm) plane meas- example a digital sensor. The lens aper- necessary to prevent camera shake and urement of light striking the fi lm emulsion ture, or opening, controls light intensity, freeze patient movements, even if a tripod allowed the camera to control the dura- while the duration of light is controlled is used. Blurring is especially a problem tion of the fl ash output, which was cut-off by the shutter speed. The aperture size is with a continuous light output such as LED once suffi cient light had reached the fi lm calibrated in f-stop numbers; the larger the illumination, halogen or tungsten lamps. for a correct exposure. However, with dig- number, the smaller the lens opening. The In these circumstances, it is vital to use fast ital sensors there is no fi lm emulsion for shutter speed is the length of time the shut- shutter speeds to ‘freeze’ the subject. On light measurements. The sensors are cov- ter remains open when the shutter release the other hand, when electronic fl ashes are ered with a protective glass that is highly is activated, expressed in fractions of sec- used, blurring is less of a concern. This is reflective, making light measurement onds, for example, 1/125 s is faster than because the duration of the fl ash light out- impossible. Some DSLRs have overcome 1/60 s. Most contemporary cameras have put is shorter (usually 1/2,000 s) than the this problem with sophisticated electron- automatic exposure, which calculates the camera shutter speeds, and the subject is ics, but others have yet to reach a practical shutter speed once the aperture is set (in ‘frozen’ by the sudden burst of light rather solution. If this is the case, two options aperture priority mode metering). than the opening of the camera shutter. are available to ensure correct exposure. However, with dental photography Most electronic fl ashes require that the The fi rst is to set the fl ashes to automatic two aspects require attention. The fi rst is shutter speed be set to synchronise with the mode, which calculates the exposure by ensuring an adequate depth of fi eld, which fl ash output and depending on the camera emitting an infrared beam directed to the leaves little latitude but to select a small manufacturer and type of lens, this varies subject to gauge lighting conditions. This aperture opening, usually f22. The second from 1/60 s to 1/250 s and is represented is satisfactory for photographing distant 64 BRITISH DENTAL JOURNAL VOLUME 207 NO. 2 JUL 25 2009 © 2009 Macmillan Publishers Limited. All rights reserved. PRACTICE subjects, but due to the proximity of the lens to the subject in macro–photography, the infrared beam misses the intended sub- ject and the image is often under-exposed. The other option to consider is increasing the exposure factor. As a lens moves closer to the object, as in close-up photography, the exposure increases exponentially. For example, for a 1:1 magnifi cation, the exposure increase factor is four. Consequently, in order to obtain a correctly exposed image, one or more of the following need adjusting: 1.