Focusing on F-Stops

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Focusing on F-Stops

From: Dummies.com:

You may have noticed that while using your video camcorder, you use the focus mechanism on your lens more than any other camcorder feature. Focusing is about the most basic function that is performed by your camcorder (either automatically or manually). With just a little knowledge and practice, you can turn focusing into a powerful technique for getting the most out of every shot. The first thing that you should practice is controlling the depth of focus (the amount of focused space in front and behind your subject). You adjust the f-stop to achieve depth of focus.

Aperture equals focal length divided by the diameter of your lens. The setting of the aperture is referred to as the f-stop.

The depth of focus directly relates to the f-stop. The higher the f-stop, the greater the depth of focus. At higher f-stops, therefore, the perception of being in focus exists for a substantial distance on either side of the actual plane of focus (the focal plane). Perception of focus means that only a very thin plane is ever actually in focus. The larger the depth of focus, the more the objects in front and behind the focal plane look like they are in focus. Higher f-stops mean that more of the shot appears to be in focus, but the shot also requires more light.

The opposite is true for depth of focus at lower f-stops. The lower the f-stop, the lower (or shallower) the depth of focus. This means that at lower f-stops, the perception of a shot being in focus is nearly nonexistent on either side of the focal plane. A typical situation in which you use a lower f-stop (for a shallower depth of focus) is when you want to blur out a background for some reason. Using lower f-stops require less light for the shot.