A Focus on Focus (page 3)

It is a rare camcorder that allows you to focus by manually turning a lens element directly. In many cases, you might press a button or dial a wheel to focus. Even if you can adjust the focus using a ring on the barrel of the lens, it usually only transmits an electrical impulse that runs the motors that control the focus. A true mechanical focus is best. Usually you can tell what you have by the feel, by the fact that the focus ring has a limited range (i.e. it doesn't go around and around in the same direction) and by the distance markings on the barrel. These markings allow professionals to rack focus almost instantly without even looking in the viewfinder. Using the focus motors on most cameras does not allow such lightning and accurate adjustments. Unfortunately, manual lenses are expensive, and therefore rare, in sub-$5,000 camcorders.

The size of your camera's iris or aperture is measured as a ratio called an "f/stop." As a ratio, it is obvious that 1/22 (0.045) is much smaller than 1/1.6 (0.625). On a camera's lens barrel or on your camcorder's LCD, the ratio is dropped and only the denominator remains: numerically 22 is larger than 1.6. So, although it is counterintuitive, you open up your iris and make it larger by selecting lower f/stop numbers.

One trick some folks use to set the focus on their camcorders is to put the camera in autofocus mode, let it focus the shot and then turn off the autofocus, effectively locking it down. Some cameras even have a button you can press and release to focus without switching into autofocus mode. Don't let some snob tell you that this is cheating: if it works for you, it's good enough for us. Whatever you do, in most situations, it is still highly recommended that you get your camera out of autofocus mode while shooting, to avoid those unintentional times when the camera hunts around for something to make sharp.

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