How to Select the Right Telecentric Lens for Your Machine Vision Application

How to Select the Right Telecentric Lens for Your Machine Vision Application

When designing a machine vision system for precise measurements or distortion-free imaging, choosing the right telecentric lens is crucial. In this blog, we explain what a telecentric lens is and how to select the right lens step-by-step for your application.

What Is a Telecentric Lens and Why Use One?

A telecentric lens is specially designed to eliminate perspective distortion. Unlike standard lenses, the image scale remains constant regardless of object distance within a specific working range. This makes them ideal for applications in metrology, quality control, and precision inspection.

Advantages of a Telecentric Lens

• Distortion-free imaging – essential for accurate measurements

• Constant magnification over depth – regardless of object position

• Sharp silhouettes with backlight – for precise edge inspection

• Less sensitive to height variations – improves repeatability

• Ideal for high-precision applications – in industries like medical and semiconductor

Step-by-Step Guide: Selecting the Right Telecentric Lens

Step 1: Calculate Sensor Dimensions

Formulas:

• Sensor width = Number of horizontal pixels × pixel size

• Sensor height = Number of vertical pixels × pixel size

Example with 4096 × 3000 pixels and 3.45 µm pixel size:

• Sensor width = 4096 × 3.45 µm = 14.14 mm

• Sensor height = 3000 × 3.45 µm = 10.35 mm

• Sensor diagonal = √(14.14² + 10.35²) ≈ 17.5 mm

Step 2: Determine the Required Magnification

Magnification (M) = Sensor width / Desired F.O.V.
Example: 14.14 mm / 130 mm ≈ 0.109×

Step 3: Determine the Minimum Required Optical Resolution

Minimum resolution = 1 / (2 × pixel size)
For 3.45 µm pixels: 1 / (2 × 0.00345 mm) ≈ 145 lp/mm
The lens should have at least MTF30 ≥ 145 lp/mm.

Step 4: Choose the Lens

Key considerations:

• Magnification around 0.11×

• F.O.V. at least 130 mm

• Resolution ≥ 145 lp/mm

• Suitable for sensor diagonal of approx. 17.5 mm

• Compatible with working distance, mounting, and illumination

Application Examples

• Metrology: Inspection of metal parts, connectors

• Backlight inspection: Shape control of glassware, packaging

• Electronics: Dimension measurement of PCB components

• Medical: Inspection of catheters, needles, and tubes

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