What are the advantages of focus tracking zoom lenses? 

Compared to a fixed focus lens, which just covers a single focal length, a zoom lens covers a wide range of focal lengths. The ability to capture many different focal lengths with a single lens is invaluable. Zoom lenses allow you to adjust focus within a stated focal length range. This is typically done by pointing the camera at an object, setting the zoom position and then focusing to achieve a sharp image. Whilst this is a great solution for capturing still images it poses an issue for video recording as you would spend a great deal of time trying to frame and focus the image. 

A focus tracking zoom lens is necessary for any application where live images are required, or you need constant focus within a range of distances. Zoom tracking involves the automatic adjustment of focus in response to zoom movements for the purpose of keeping an object of interest in focus. A focus tracking zoom lens is designed to maintain focus at any point within its focal length range. Zoom tracking is important when users want their subjects always in sharp focus even when they are zooming in or out. A tracking zoom lens does not require auto focus once tracking is set and a well-designed tracking zoom will maintain good resolution and focus throughout the zoom range.

Focus tracking zoom lenses are used in many applications including broadcast TV, CCTV, machine vision, nuclear monitoring, and military surveillance. Different applications require different solutions. Broadcast TV may demand high resolution from a very compact zoom. Military applications typically require the zoom to be rugged and able to withstand shock and vibration. Nuclear applications require the zoom to be radiation resistant utilising special glass types to avoid discolouring when exposed to radiation.

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