Zoom lens
Zoom lenses are advanced vario lenses. We can vary their focal length (colloquially, "to zoom" the lens) and they remain focused. In the case of manual zoom lenses this is ensured opto-mechanically. Therefore they are quite big, weighty and expensive.
In the case of industrial USB cameras, FireWire cameras or GigE cameras with integrated lenses (like the zoom cameras from The Imaging Source), the readjustment of the focus is performed by software.
Important: Besides their size and weight, manual zoom lenses have another disadvantage. Their minimum object distance is usually one meter or even more. In contrast to fixed focus C-mount lenses, the minimum object distance cannot be reduced by extension rings: The lens would lose its capability to readjust the focus after it has been zoomed.
Therefore, manual zoom lenses are rarely used in machine vision systems.
