Imagine pushing a magic button that allows you to see three dimensionally through a tooth; you see caries, cracks, and more…
I was recently giving a photography course at Dr. Ernie Casares office in San Diego, California. When we were finished he showed me a very cool gadget called a MicroLux Trans Illuminator. He puts its condensed LED light behind the patients tooth and it turns the tooth from opaque to translucent, revealing cracks, craze lines and fissures. Wow – Everything lights up like a Jack-O-Lantern! Dr. Casares says it also reveals subgingival calculus and the root canal orifice. I am not a dentist but might find it thrilling to see a root canal orifice. But I digress…
We thought it would be exciting and educational to take a picture of the event for documentation and patient show and tell, but we found it to be challenging.
You have to have some working knowledge of camera controls to translate what a picture is telling you. In essence, we were trying to photograph a bright light, like a star in the night sky. The images using the cameras close up settings did not come out clearly, but after we made a few adjustments we figured out the optimal settings to take a high light-contrast photo.
I knew right away to turn the cameras flash off because the tooth was much too illuminated to see anything of value. Viewing it through my own eyes the tooth was a bit too bright to see a lot of detail, which tells me I need to adjust two settings.
The two settings are aperture and shutter speed. Together, they affect depth of field and how much light is allowed to come through. We put the camera in “aperture” priority (Av) which allows us to adjust how much light will enter the shutter, similar to how a person’s irises work. The camera will decide on the shutter speed. Initially, the photo results were not good; the light caused the illuminated tooth to be over exposed and the rest of the picture to be under exposed.
An analogy would be a performer on a stage being lit by a spotlight. A majority of the surrounding stage is dark. You take a picture and find that the performer, the subject you want to see, is over exposed, they look white. It is not the cameras fault; it simply balances the amount of white to dark and sets an exposure.
The opposite occurs when the majority of the background is white. Your target will appear darker than it actually is. This may occur when you are in the snow or if you have a powerful flash that reflects too much off of the surroundings.
The solution was to use the cameras “exposure compensation [Ev].” This feature over-rides the shutter speed and or aperture settings, making them either shorter or longer than what is normal for the camera. So, if you want the picture darker, which was the case because the lit tooth was over exposed (too white), you go from zero towards the minus side. We set the Ev to a -2 (minus 2) and got great results.
1. Aperture priority (put your camera in Av or A)
2. F-stop 5.6
3. ISO was 80
4. Flash Off
5. Exposure compensation at -2 or a similar setting
6. Normal lighting in the operatory
7. Keep your hand steady to compensate for the slower shutter speed
8. Zoom the camera to encompass about 8 teeth
Other situations where camera knowledge comes to play is VelScope Photography and taking portraits of people of dark complexion.
[ http://digital-photography-school.com/ev-compensation-explained ]