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The eld of view can be classied into three types:

> Normal view: oering the same eld of view as the human eye.

> Telephoto: a narrower eld of view, providing, in general, ner details than a human eye can

deliver. A telephoto lens is used when the surveillance object is either small or located far

away from the camera. A telephoto lens generally has less light gathering capability than a

normal lens.

> Wide angle: a larger eld of view with less detail than in normal view. A wide-angle lens

generally provides good depth of eld and fair, low-light performance. Wide-angle lenses

sometimes produce geometrical distortions such as the “sh-eye” eect.

Figure 3.2a Dierent elds of view: wide-angle view (at left); normal view (middle); telephoto (at right).

Figure 3.2b Network camera lenses with dierent focal lengths: wide-angle (at left); normal (middle); telephoto (at

right).

There are three main types of lenses:

> Fixed lens: Such a lens oers a focal length that is xed; that is, only one eld of view

(either normal, telephoto or wide angle). A common focal length of a xed network camera

lens is 4 mm.

CAMERA ELEMENTS - CHAPTER 3

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Axis Network video Specifiche Pagina 29