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In Focus: Microphotography using the Dental Operative Microscope by Jorge Zapata, DDS

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These challenges include: controlling the vibration of both the microscope and the camera, working in conjunction with live view monitors, and understanding the par-focal adjustment of the microscope to assure clear focus of both the camera and microscope. Avoiding vibration

In microphotography, many different sources of vibration can affect the sharpness of pictures, and each must be isolated and eliminated in order to capture the highest-quality images.

In Fig. 1, (pg. 38) dots and thin, short, horizontal lines can be noted. These distortions create the sensation that the picture is moving sideways. This perceived motion is the result of one or more of the following factors:
  • Vibration in the body of the microscope
  • Tremor of the clinician's hand while holding the dental mirror
  • Shaking of the patient's jaw
  • Vibration related to the movement of the internal mirror of the camera (SLRs) at moment of shutter release.
Some of the vibration can be improved and controlled by the clinician. However, some vibration will continue to exist, despite the clinician's best efforts to overcome it. Vibration of the scope's body is nearly impossible to eliminate. Other vibration can be improved with the use of surgical armrests, a mouth prop, a remote control and a fast shutter speed of at least 1/125 and above.

Out of focus
The desire of every photographer is that each picture captured will be clear, and every detail in the given subject accurately reproduced; any tiny movement can affect the final result of the image. The photographer can correct for vibration, but the camera may still capture images that are not sharp because of focus issues.

So how can the photographer take pictures that are sharp and full of the desired detail? What specific techniques do professional photographers use to capture acute images? Sometimes the photographer will find that when the focus is set on the foreground of the subject, the background goes out of focus, and vice versa. The answer to this dilemma is to use the depth of field (DOF) correctly. Photographer Bryan Peterson defines this in his book, Understanding Exposure, as the area of sharpness (from near to far) within a photograph.

It is important to understand DOF in microphotography in order to control image sharpness. In microphotography, the DOF is very shallow, so missing the focus point by even a millimeter causes the pictures to be out of focus. The DOF is impacted by the level of magnification. For example, lower magnification produces more DOF, as demonstrated in Fig. 2. Whereas Fig. 3 shows that higher magnification has a narrower DOF.





Selecting the focus point
Because the DOF is so restricted when shooting under the microscope, the focus point has to be the sharpest spot in your picture. Before capturing an image, it is necessary to think like a photographer and ask yourself some questions:
  1. Why do I want to capture this picture?
  2. What is the point of interest in this image?
  3. What do I want the viewers to see in the image?
  4. How is this image going to be different from others?
  5. Where do I want to focus?
This is my formula: Find the things in the image that stand out as being most important, and place the focus point there. For example, in Fig. 5, I wanted to capture the gutta percha in the mesial buccal canals. Therefore, I selected my focus point as the tiny white spot in the DB canal. The important parts of the picture were in focus.

Working with live view
Live-view mode is a useful tool in successful microphotography. One of the significant advantages to using live view in DSLR cameras is that the camera's internal mirror will be flipped up, allowing you to display on your LCD or monitors exactly what your camera is seeing.

Because the mirror is raised up when working in live view, the camera does not cause vibration of the scope, so the microscope's bounce is decreased and sharper images are obtained. Mirrorless and translucent cameras always display live view. Live-view display gives significant help in achieving sharply focused pictures, and the assistant can confirm that the image is centered and focused prior to capturing the final image.

Live view also allows the photographer to easily readjust the settings because he or she can quickly check focus, framing, etc.

For example, in Fig. 6 on p. 41, the image is out of focus, the framing is off, the picture is overexposed, the ISO, white balance and the shutter speed are not ideal. After readjusting the settings in live view, the final result was greatly improved (see Fig. 7 on p. 41).



Perfecting focus
The real key to successful microphotography is to find the precise balance between the camera and the microscope. In other words, the subject that is observed through the eyepieces of the DOM must be perfectly duplicated by the camera, without any distortion. Par-focal adjustment is crucial to success in microphotography.

This desired outcome is accomplished through correct par-focal adjustment of the microscope. Par-focal adjustments assure that the image is in focus under the DOM and camera simultaneously, and when magnification is changed from higher to lower (or vice versa), the object stays in focus.

However, if we follow the typical guidelines to make the par-focal adjustments, the image as seen through the microscope will be clear, but will reproduce as blurry in photographs. This unwanted result occurs because the manufacturer's par-focal procedures indicate the use of a two-dimensional, flat target as point of reference.

Translation of these adjustment settings to the mouth of the patient results in pictures that are out of focus because the open mouth of the patient is triangular in shape, as demonstrated in Fig. 8, but par-focal adjustments were made using the flat target. Therefore, it is necessary to set the camera and DOM using a three-dimensional target, which recreates the position of the open mouth. Successful setting of the DOM and camera can be accomplished by constructing a three-dimensional focusing target that mirrors the angles and dimensions of a mouth-propped patient.



Finally, set the camera to center metering mode (CMM), put the focus point on a small dot on your custom PF target and, working with monitors, center the image in the middle of the screen. Next, follow the traditional steps as outlined by your microscope company for par-focal adjustment. Fig. 9 is an example of a photograph where par-focal adjustment has been done incorrectly.

Fig. 10 is a picture taken with correct par-focal adjustment.

Conclusion
Microphotography is an art, and in order to capture the highest-quality pictures it is necessary to understand the obstacles that will be encountered and how to overcome them. The photographer must achieve the perfect balance between the microscope and camera in order to get the desired results.

References
  1. Peterson, Bryan (2010). Understanding Exposure. (3rd Edition, p. 42). New York: Crown Publishing Company




Dr. Jorge Zapata is a dentist in Ogden, Utah, who has been practicing microscope dentistry in his private dental practice since 2005. Dr. Zapata is treasurer of the Academy of Microscope Enhanced Dentistry (AMED). He has been a member of the board of directors for AMED since 2011, and in 2014 he was a recipient of AMED's Outstanding Service Award. Zapata was a guest lecturer at Roseman Dental School in Salt Lake City in 2015 and was a guest speaker at the European Society of Microscope Dentistry in Berlin. He can be contacted at zapata_dental@yahoo.com.


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