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# Selecting the Right Zoom Lens

Choosing the right machine vision lens is critical for achieving optimal performance in imaging applications. This guide covers the essential parameters and considerations for selecting a zoom lens, ensuring it meets specific application requirements.

## Fundamental Parameters

To select the appropriate imaging lens, it’s essential to understand the basic components of an imaging system. Key parameters include:

• Working Distance (WD): The distance between the lens and the subject.
• Field of View (FOV): The area that the lens can capture.
• Resolution: The level of detail the lens can capture within the given FOV.

These parameters must align with the requirements of your application to ensure optimal visual performance.

## Selecting the Lens

When choosing a lens, it’s assumed that a camera has already been selected, narrowing down the lens options. Both fixed focal length and zoom lenses operate on the same principles, allowing for a similar selection process. For zoom lenses, ensure the zoom function is locked at various focal lengths.

## Key considerations include

Optical Specifications: Ensuring the lens meets the WD, FOV, and resolution requirements.

• Mechanical Dimensions and Cost: Assessing these factors in relation to your application’s needs.

## Image Formation by Thin Lenses

The basic lens equation (1/f = 1/do + 1/di) helps determine focal lengths for simpler setups. In this equation:

• di: Image distance (distance from the image plane to the last lens element).
• do: Object distance (distance from the object to the front lens element).
• f: Focal length of the lens.

This equation is useful for simple lens systems but is insufficient for complex machine vision systems with multi-element lenses.

Equation 3, derived from the basic lens equation, provides a quick way to determine the required focal length for a lens given the FOV and sensor size. This simplifies the lens selection process significantly, especially when using online lens calculators.

## Considerations for Fixed Focus Lenses

Fixed magnification lenses, like telecentric or microscope objectives, may seem complex but are easier to integrate than traditional lenses. These lenses typically operate at a specific WD and are characterized by their magnification, which is physically labeled on the lenses. The FOV can be determined using the following equation:​

Where:

• m: Magnification specified for the lens.
• ho: Sensor size.

For measurement applications, a telecentric lens with the appropriate magnification should be chosen.

Careful consideration of WD, FOV, and resolution, along with a proper understanding of lens equations, ensures the selection of the most suitable imaging lens. This approach guarantees optimal performance for your specific application, whether using a zoom or fixed focus lens.

Contact Shanghai Optics today! We’d be more than happy to discuss your projects and how to best bring them to fruition.