When the view needs a lens the integrated cameras do not offer, or the environment needs a housing they cannot provide.

Very long views, very wide views in confined spaces, and views where the subject must be a specific size in the frame are all lens problems.

Low-light scenes benefit from large-aperture lenses that are simply not fitted to integrated cameras.

Extreme temperature, wash-down, corrosive and hazardous-area environments need specialised housings.

For an ordinary view in an ordinary environment, an integrated camera is cheaper, faster to install and perfectly adequate.

The rule of thumb: if a standard camera's lens range covers the view, use a standard camera.

The lens mount, the image circle against the sensor size, the iris control type, and the physical space inside the housing.

Mount type determines whether the lens screws on at all, and adaptors exist but change the back focus.

The image circle must cover the sensor. A lens designed for a smaller sensor produces dark, soft corners on a larger one.

Iris control differs - manual, automatic driven by the camera, or a motorised iris - and the body has to support the type fitted.

Housing dimensions matter physically: a long telephoto lens may not fit, or may not leave room for the connectors.

Check all four before ordering. Discovering the mismatch on site means a return and a second visit.

It is the distance between the lens and the sensor, and it has to be adjusted on site so the image stays in focus across the zoom range and at night.

With an interchangeable lens the alignment is not set at the factory, so it is part of commissioning.

Incorrect back focus shows as an image that is sharp at one zoom setting and soft at another.

It also shows as a picture that is focused in daylight and soft at night, because infrared light focuses at a different point than visible light.

Infrared-corrected lenses solve the day-night shift optically and are worth specifying on any camera with night-time illumination.

Set focus at night if night footage matters, since that is the harder condition and the one people actually need.

Heated, cooled, wash-down, explosion-protected, pressurised and pole or corner mounted housings - most of them impossible with an integrated camera.

Heated housings keep the camera above its minimum operating temperature and keep the window clear of ice and condensation.

Cooled and sun-shielded housings extend the range at the other end.

Wash-down housings in stainless steel suit food production and pharmaceutical areas cleaned with high-pressure water and chemicals.

Explosion-protected housings are certified for hazardous atmospheres and must be selected against the specific zone classification, which is a regulated matter.

Pressurised housings keep corrosive atmospheres out entirely and are used in chemical and marine environments.

For specialist applications, yes - integrated cameras have absorbed most ordinary work, but nothing else solves an unusual lens or housing requirement.

Modern dome and bullet cameras cover a wide zoom range and most environments, which is why they dominate general installations.

Where the requirement falls outside that range, there is no substitute.

Traffic, rail, industrial process monitoring and long-range perimeter views are the recurring cases.

They also remain useful where a camera must be housed in something specific for regulatory reasons.

Availability is narrower than it was, so check the lens and housing supply chain before standardising on a body for a large project.