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To Zoom or Not to Zoom

A zoom lens can overcome many hurdles faced by machine vision applications, whether they require a vastly changing field-of-view or precise magnification. But is it the best choice for every application?

by Greg Hollows

May 2003

Zoom lenses run the gamut of field-of-view (FOV) and magnification ranges. Some are designed for high magnification applications commonly found in semiconductor inspection, while others are geared toward the larger FOVs used in security applications. What they all have in common is the ability to change the field without varying the working distance. With a fixed focal length lens, the distance between the lens and the object must be physically changed in order to achieve a different FOV. This means that zoom lenses offer some great advantages. Imagine if, in a security application, a camera and lens had to move from a safe distance to within a few feet of an object or individual in order to see more detail. It would not be practical, let alone cost-effective.

Zoom lenses offer the ability to change magnification without changing working distance. Additionally, many zoom lenses can perform over a range of working distances while providing the same magnification. To achieve the same result without a zoom lens, a system would require multiple fixed focal length lenses.

A Certain Point-of-View
The drawbacks to using a zoom lens should also be considered. The optical and opto-mechanical design of zoom lenses are more complicated than the designs for most fixed focal-length lenses. This results in higher costs for materials, machining, and assembly. Generally speaking, zoom lenses cost much more than their fixed focal length counterparts.

Another concern is that while zoom lenses can provide many different working distances, the overall image quality produced at any given setting may not be sufficient for the application. Fixed focal length lenses designed to meet specific working distance requirements may suit an application better.