PTZ or not?

Q: When I'm planning CCTV installations, do I still need to consider PTZ cameras, or is it now OK just to use domes?

A: Modern domes are very capable, but there are applications where PTZ cameras are more appropriate. Important factors to take into account include, for example, lens parameters. Domes utilise modular camera/lens combinations with up to 30x optical zoom in some cases. However, overall quality is rarely as accurate as a bespoke camera/motorised lens combination housed within a PTZ head.

Q: Can digital zoom be used to extend the zoom range of a dome?

A: Be careful! Digital zoom can only enlarge what the camera has already captured. It may make distant objects easier to see but, unlike optical zoom, it doesn't actually help to capture extra detail. This is important when, for example, facial recognition is required. With digital zoom, you may be able to make a face fill your screen, but it may be too blurred to recognise.

Q: Is image distortion always an issue?

A: Domes will always produce somewhat poorer pictures under certain circumstances because of the distortion introduced by the curvature of the hemisphere. However, in good light and at reasonable zoom ratios, the difference in quality between the pictures produced by a dome and those produced by a PTZ can be negligible, particularly if you use larger 7 inch domes which give better optical performance.

Q: You mention good light. Does that mean light levels are also a factor?

A: Yes, always. Domes utilise modular cameras which are not quite as good at coping with low light conditions. Usually the result is more noise in the images at low light levels. This not only makes it harder to see what's going on, it also makes the images harder to compress, which means they take up more hard disk space on a digital recorder.

Q: Are there any other factors to consider?

A: Cost and durability. Domes cost less and are easier to install, but they're less durable and harder to clean. Wash/wipe can, for example, be added to clean the glass of a PTZ camera, which still cannot be achieved using a standard dome. To sum up, a dome will suffice in most CCTV applications. However, when considering high quality image reproduction, excellent low-light performance, supplementary IR lighting and harsh operating environments, I would recommend the use of a PTZ.