In the fields of machine vision and industrial inspection, telecentric lenses have become indispensable tools for measuring high-precision workpiece dimensions. Their unique parallel optical path design effectively eliminates perspective distortion. But how can you quickly calculate the required lens magnification based on workpiece dimensions and camera parameters? This article will guide you through a straightforward three-step method to effortlessly solve this challenge!

Step 1: Determine the maximum dimensions (field of view) of the test object.

Core Question: How large an area of the workpiece does your lens need to “see”? This step forms the basis of the calculation.

The maximum length or width of the workpiece (e.g., the long side of a rectangular part is 50mm); whether additional edge clearance is required (e.g., for fixtures or background, typically recommending a field of view 10%-20% larger than the workpiece).

Example: If the workpiece's maximum dimension is 50mm and 5mm of edge clearance is required, the actual field of view (FOV) should be 55mm.

Step 2: Confirm the camera's sensor size

The core question: How big is your camera's “eye”?

Sensor size directly impacts the imaging range. Common sensor dimensions (diagonal or width/height) must be obtained from the camera specification sheet, with common formats including:

• 1/2 inch (approx. 6.4mm × 4.8mm, diagonal 8mm);
• 2/3 inch (approx. 8.8mm × 6.6mm, diagonal 11mm);
• 1 inch (approx. 12.8mm × 9.6mm, diagonal 16mm).

Note: If the sensor is rectangular, specify whether the long or short side is used for calculations (typically corresponding to the field of view direction). For example, if the field of view is 55mm horizontally, use the sensor's horizontal dimension (e.g., 6.4mm).

Step 3: Apply the formula to calculate the range of multipliers.

Core Formula: Magnification Factor (β) = Sensor Size (in Corresponding Direction) / Field of View (FOV)

Calculation Steps:

1. Standardize sensor dimensions and field-of-view units (typically in millimeters);
2. Substitute into the formula for calculation.

Example:

• Sensor horizontal dimension: 6.4mm
• Field of view (FOV): 55mm
• Magnification ratio β = 6.4mm / 55mm ≈ 0.116 (i.e., 1:8.6, indicating an 8.6x reduction in image size)

Interpretation of Results:

• If the calculated result is 0.116, it means the lens must reduce the 55mm field of view to fit within the sensor's 6.4mm range.
• When selecting an actual lens, choose one with a magnification ratio close to but slightly less than the calculated value (e.g., 0.1x or 1:10) to avoid insufficient field of view.

Further Reflection: Why “slightly smaller than”?

The nominal magnification of a telecentric lens is typically an ideal value. In actual use:

• Too low magnification: The field of view is too large, causing the workpiece to occupy too small a proportion in the image and reducing measurement accuracy.
• Too high magnification: The field of view is insufficient, causing part of the workpiece to extend beyond the frame.
• Therefore, selecting a magnification slightly lower than the calculated value allows for adjustment leeway. Simultaneously, fine-tune the imaging effect by adjusting the working distance (the distance between the lens and the workpiece).