Focal Length of CCTV Camera

Focal length is the lens property that decides how wide or narrow a camera's view is. A lens with a shorter focal length gives a wider view, covering more of a scene with less detail per part of it. A lens with a longer focal length gives a narrower view, covering less of a scene with more detail for the part it does cover.

This guide explains the idea in plain language for CCTV camera buyers. It states no focal length figure for any lens, because figures belong to a model specification, and no model specification is published on this site. The guide's purpose is to give buyers the vocabulary to describe the view they need, so that an inquiry can be answered properly.

What focal length does to the picture

Think of focal length as the width control for the camera's view. Turn it one way and the camera sees a whole room but shows each person in it small. Turn it the other way and the camera sees one doorway but shows it large. Neither setting is better in itself; the right setting is the one that answers the buyer's question about the scene.

That question should be asked before the lens is chosen: must the picture show a whole area, a particular point, or both at different times? A whole area points toward a wider view. A particular point points toward a narrower view. Both at different times points toward an adjustable lens, such as a varifocal or zoom lens.

How to describe the view you need

A useful description names the scene, the camera position, the area or point to be covered, and what the picture must show. For example, a buyer might say the camera sits over a yard entrance, must show the whole yard in general, and must also show the gate clearly enough to recognise what passes through it. That description already contains the focal length question, even without numbers.

A description that only says wide or narrow, without the scene, is harder to answer. The same width of view covers a small room completely and a large yard only partly, so the scene and the position matter as much as the width word.

Common mistakes in choosing a view

One common mistake is choosing the widest view available, on the grounds that more coverage must be better. A very wide view can leave every part of the scene too small to be useful, so the camera watches everything and shows nothing clearly. Another common mistake is choosing a narrow view for a whole area, which leaves most of the area unwatched.

A third mistake is fixing the view before the camera position is fixed. The view depends on the position, so a buyer who changes the position after choosing the lens may find the view no longer fits. Fix the position first, or choose an adjustable lens and set the view after installation.

Frequently asked questions

Does a longer focal length mean a better lens?

No. It means a narrower view with more detail for the part covered. Better depends on what the picture must show.

Can I work out the view without numbers?

You can describe it: the scene, the position, the area or point, and what must be visible. Numbers belong to the model specification, which must be confirmed for the exact lens offered.

What if I need both a wide view and detail?

Consider an adjustable lens, or two cameras: one wide for overview and one narrow for the point of interest.

Related pages

• CCTV Camera Lenses
• Varifocal Lenses
• Wide-Angle CCTV Cameras
• Lens Used in CCTV Camera Guide