How to Choose a CCTV Lens

Choosing a CCTV lens looks simple from the outside: a camera needs a lens, a lens is fitted, and a picture appears. In practice the choice decides what the camera can actually show, and a lens chosen without describing the scene will often show the wrong thing, too wide to pick out detail or too narrow to cover the area. This guide walks through the choice step by step, so that a buyer can describe the job properly and ask for a lens that fits it.

The guide assumes no prior knowledge of lenses. It explains the ideas in plain language, it states no model and no specification, and it ends with an inquiry checklist, because the final step in choosing a CCTV lens is always the same: describe the camera and the scene, and confirm the exact lens, its specifications, its terms and its documents in writing before payment.

Step one: name the camera

The first step is to name the camera the lens will be fitted to. A CCTV camera, an industrial camera and a board camera use different lens families, and a lens that fits one will not necessarily fit another. The company's listed categories on this site reflect that division: CCTV lenses for CCTV cameras, C Mount industrial lenses for industrial cameras, and M12 board lenses for board cameras and small modules.

Naming the camera also means naming the mounting arrangement, if it is known. The mount decides whether a lens can be fitted at all, before any question of picture quality arises, and a buyer who omits the mount from an inquiry risks being offered a lens that cannot be used. If the mount is not known, say so, and describe the camera as fully as possible, so that the supplier can help identify the fitting.

A buyer who is replacing a lens should also describe the existing arrangement: what is fitted now, what works about it, and what does not. A replacement that repeats the old lens's view will repeat the old lens's problems, while a replacement chosen without knowing the old view may create new ones. The existing lens, if it can be described, is useful evidence, not a detail to be hidden.

Step two: describe the scene

The second step is to describe the scene the camera must cover. A scene description names the place, the camera position, the area or point to be watched, and the light. A camera over a yard entrance faces a different scene from a camera in a corridor, and a camera watching a shop floor faces a different scene from a camera watching a car park, even if both cameras are the same model.

Light deserves its own sentence in the description. A scene that is bright at midday may be dark at night, a scene facing a bright entrance may be washed out while the interior stays dark, and a scene outdoors changes with weather and seasons. A lens choice made for an ideal scene may fail in the real one, so the inquiry should describe the real light, not the light on a showroom wall.

The scene description should also say what must be visible and what may be ignored. A camera that must show a whole room needs a different view from a camera that must show a doorway, and a camera that must show both at different times needs an adjustable lens. Naming the must-see parts of the scene, and the parts that do not matter, is the fastest way to narrow the lens choice.

Step three: decide what the picture must do

The third step is to decide what the picture must do. A picture that only needs to show whether someone is present asks less of a lens than a picture that must show who that person is, and a picture that must support a measurement asks more than either. Buyers often describe the camera and the scene in detail but never state what the picture is for, and the lens choice then becomes a guess.

Three questions cover most jobs. Must the picture show a whole area, a particular point, or both at different times? Must it show detail at a distance, or only general movement? Must shapes in the picture stay true, for measurement or analysis, or is a general view enough? The answers to those three questions point to wide, narrow, adjustable or low distortion lenses respectively, and they should be stated in the inquiry.

Where the picture must do two things at different times, an adjustable lens, such as a varifocal or zoom lens, should be considered. Where the picture must always do the same thing, a fixed view may be simpler and more repeatable. The varifocal versus fixed guide on this site explains that trade-off, and it is worth reading before deciding, since adjustment is useful only where the view genuinely needs to change.

Step four: confirm the exact lens before ordering

The fourth step is to confirm the exact lens, if one is offered, together with its specifications, in writing. This site publishes no model list and no specification table, so the confirmation must come from the supplier, for the exact lens concerned, against the camera and scene described in the inquiry. A general assurance that a lens will suit the job is not a confirmation.

Confirm the commercial terms at the same time: the minimum order quantity, the lead time and the price for the quantity required, and what the price includes and excludes. Confirm which documents are supplied with the order. On this site the certificate position is stated plainly: Certificates available upon request. No certificate name, number or issuing body is stated here, and none should be assumed.

Finally, confirm compatibility with the camera and mounting arrangement, in writing, before payment. Compatibility is the one failure that cannot be worked around after delivery: a lens that does not fit cannot be adjusted into fitting, however good its view might have been. The inquiry checklist at the end of this post repeats every confirmation in one place, so that nothing is left to memory.

Frequently asked questions

What is the most common mistake when choosing a CCTV lens?

Choosing the view before describing the scene. Fix the camera position and the scene first, state what the picture must show, and let the lens follow those answers.

Do I need to know lens terminology to choose?

No. A clear description of the camera, the scene and what the picture must do is more useful than any technical term, and it lets the supplier recommend a lens that fits the job.

Can I choose from this site alone?

This site explains the choice and the categories, but it publishes no models or specifications. The final choice must be confirmed with the supplier for the exact lens offered.

Related pages

• CCTV Camera Lenses
• CCTV Camera Focal Length Guide
• Varifocal Lenses
• Lens Used in CCTV Camera Guide