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.

Advanced Calculations

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.