Sunday, April 22, 2012

Why Great Depth of Field is Important in Dental Photography

Yeah, yeah, I know. Most dentists just want to pick up a camera, point it and get great images. So, if that's the case, then why all the fuss over depth of field?

Years ago, when we shot dental images on slide film, we were told to "focus on the laterals" so that we could get the centrals and cuspids in focus. With the advancement of technology, more specifically flash technology, we suddenly had a way to get a ton of lighting on an area, forcing us to turn the f-stop way up to give us great images.

But what's an f-stop and why does it matter?

f-stops, or apertures, are the adjustable components of the camera that allow light into the camera. The higher the number, the less light it lets into the camera. However, the higher the number, the greater the depth of field. A higher depth of field means that more is in focus from front to back. So, an f-stop of 32 will have much more in focus than an f-stop of 5.

For clinical photography, a higher depth of field means that for certain images we can worry less about having to focus perfectly and we will still get more in focus. For instance, for an anterior retracted image such as the one below, an f-stop of 25 will allow us to get every tooth, from central to 2nd molar in focus. Better yet, when shooting a high f-stop, it means that if you're off a bit in terms of your focus, you can get away with it because you have 2-3 inches of "depth" to play with.

With a higher f-stop, all teeth are easily in focus.
When one doesn't manage the f-stop properly, depth of field can be diminished.  Let's say you shot an image with an f-stop of 9, you will see a considerably diminished depth of field.

Notice how the posterior teeth are out of focus with this low f-stop image

So, the key is to be able to control your f-stop and always shoot with as high of an f-stop as possible for any given situation.  Sometimes, like for full face images, distance from subject requires all the flash power you can muster, as opposed to images such as a single central when there isn't a f-stop high enough to manage the amount of light thrown out by a full power flash, necessitating a lower flash power.

The need to alter flash power and f-stop settings are just two more reasons why I have felt that "point and shoot" cameras (which do not generally have either of the aforementioned features) are simply not appropriate for dental use.

There is one exception to the rule of great depth of field and it's portrait photography. When we take an image of a full face for non-clinical use, we do not want the background in focus, so it's important to manage lighting in such a way that the f-stop used is lower than for intraoral shots.

In portrait images, photographers use low f-stops to emphasize the face and make the background out of focus.

In the future, I'll cover more aspects of this topic including how to set your camera up to do this quickly and easily.

As always, if you have any questions, feel free to email me at Glenn@KriegerContinuum.com .

Best Wishes,

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