Fixed Focus and Zone Focus Lenses

Many inexpensive digital cameras, as well as some rather sophisticated underwater models, come equipped with what is called a fixed focus lens. As its name implies, the lens is fixed, or frozen, and cannot be focused. Actually, it doesn't need to be focused because the focal length (size of the lens) is very small and consequently its depth of field typically ranges from a foot or 20" to infinity. Most fixed focus lenses are also fixed focal length lenses, meaning that they aren't optical zooms. Incidentally, to soften the stigma that cheap fixed focus lenses imply, manufacturers sometimes tout its advantage by calling it, euphemistically, a focus-free lens.

Zone focus is one rung above fixed focus on the optics scale. You can't continuously focus the lens, but by pressing a lever or a slider, you can mechanically move the front element nearer or further to the rear element at a predetermined increment, thereby changing the focus plane. Typically, a zone focus lens will have three settings: macro, portrait, and landscape. Macro is for close-ups (12"—24"), normal is for typical near shots (2'—10'), and landscape for distance (10'—infinity). The only problem is that if you switch to another setting, the lens doesn't automatically return to the previous setting, so lots of photos can end up out of focus if you forget to move the lens to match the distance to the subject.

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