In my last column I talked about the different features of the SLR digital cameras that affect how light gets to the computer chip inside the camera. This month I want to expand on one of these factors, Flash Systems.
All digital cameras come with an “on board” flash. This is the flash located either on the top of the camera or on the left side. For digital SLR cameras the flash is usually “pop up” style and a button must be pushed to open it. Point and Shoot style cameras usually have the flash already exposed and located on the top or left side of the camera. While these flash systems already found on the camera may be sufficient for recreational use, they are not always adequate for dental photography. For a digital camera to focus efficiently on a subject, it must be able to read the contrast found in the image. The better the image is illuminated, the faster the camera will focus. This is especially true for Point and Shoot style cameras. If you have ever tried to take an arch shot with a Pont and Shot style camera and it just keeps hunting for the focus then you know what I am talking about. The computer chips found in the most recently released cameras are more sensitive and require less light to focus. But additional light is still needed for intraoral photography.
The most common flash system used in dentistry with digital cameras is a ring flash. A ring flash emits light 360 degrees around the lens. This provides illumination to the subject from all directions. It is designed for close up photography. This is different from the “on board flash” found on digital cameras. The “on board” flash only gives additional lights from only one direction, usually from the top of the lens or from the left side. This causes problems in two areas. As I have already discussed it makes it difficult to take intraoral shots easily. This is because the light from the flash bounces off the cheek and lips and very little actually enters the mouth. When a smile shot or a shot taken with retractors is used the left buccal corridor will be fine but the right buccal corridor will be dark. The ring flash eliminates these problems. It emits light from all sides so enough light enters the mouth for intraoral shots. It also lights up both sides of the smile evenly. But as with everything, bad comes along with the good. The ring flash can do its job too well. Its job is to illuminate the entire field from all directions. But this will also eliminate all shadows. This means the slight texture and anatomy found particularly on anterior teeth will not be seen. So teeth and veneers may look “flat”.
A twin flash solves this problem. It has a ring which attaches to the end of the lens like a ring flash but it only has two flashes located on opposite sides. These flashes can usually be rotated around the ring and o their own axis. So they can be positioned in almost any position. I keep mine at the 9 and 12 o’clock position and pointed straight ahead. This provides light to both sides of the smile and gives enough light to illuminate an arch. But it does not remove all the shadows. A smile taken with a twin flash will look much more natural than a smile taken with a ring flash. The color quality will be the same but the slightest texture will still be visible. The down side to a twin flash is its cost. A ring flash will cost between $200 and $400 depending on the model. A twin flash will cost $700 to $1100. I have both Canon models that I use with my Canon 20D Digital SLR Camera and suggest the twin flash if it fits your budget. Both the Canon Ring Flash and Twin Flash will fit on Canon G series Point and Shoot cameras as well. For compatibility of Fugi and Nikon Ring/Twin flashes with their Point and Shoot cameras you will need to consult you camera dealer.
Another flash system that should be mentioned is the ”flash diffuser” from Photomed. It is designed to fit on the Canon G series cameras as well as other models. You will need to contact them to see if it will fit your camera. It is designed to distribute the on-board flash of a Point and Shoot style camera evenly in the same manner as a ring flash. It works very well. The down side is that it is only made for certain cameras and if you upgrade to an SLR from a Point and Shoot you will have to buy another flash.