I. Calculation of ZOOM LENS Magnification

The magnification ratio of a ZOOM LENS typically refers to its optical magnification, describing the size relationship between the subject being photographed and its image on the image plane. Its core calculation is based on focal length, working distance, and sensor size.

1. Core Calculation Formula:

Optical magnification (β)

β = f / ( u − f ) ≈ f / u ​( When u ≫ f )

Note: β: Optical magnification (unitless); f: Focal length of the lens; u: Working distance (object distance)

Physical Meaning: The magnification factor β represents the ratio of the image size to the actual size of the object. For example, β=0.1 indicates that the image on the sensor is one-tenth the actual size of the object.

2. Field of View (FOV) and Magnification Relationship

① FOVH = Sensor dimension H / β       ② FOVV = Sensor dimension V / β

Note: FOV: Field of view, i.e., the actual range within which objects can be seen; Sensor dimension: The width (W) or height (H) of the camera sensor. This is a fixed value (e.g., the width of a 1/1.8-inch sensor is approximately 7.2mm).

A practical inverse calculation formula: When you know the target field of view and sensor size, you can directly estimate the required magnification: β ≈ Sensor Size / Target Field of View Size

II. Adjusting the Magnification of a ZOOM LENS

Adjusting a ZOOM LENS typically involves two separate yet related steps.：Zoom and Focus

1. Variable Zoom Ring Adjustment

（1）Function: Adjusts the focal length (f) of the lens. When rotating the zoom ring, the relative positions of multiple lens elements inside the lens change, thereby continuously altering the focal length.

（2）Impact on the system:

• Changing magnification: Longer focal length → Increased magnification → Smaller field of view (seeing farther, narrower range);
• Changing field of view angle: Longer focal length → Smaller field of view angle;
• Changing depth of field: Typically, a longer focal length results in shallower depth of field.

2. Focus Ring Adjustment

• Function: After setting the focal length (magnification), move specific lens elements within the optical system to ensure objects at a given working distance are sharply focused on the sensor plane.

•  

  Key Principle: Zoom first, then focus. Adjust the zoom ring to achieve the desired magnification/field of view before turning the focus ring to sharpen the image.

3. Adjustment Tools and Methods

• Manual Mechanical Adjustment: Most industrial ZOOM LENSES feature lockable zoom and focus rings, adjustable and lockable using an Allen wrench or direct manual rotation.

• Motorized Servo Adjustment: Used in high-end or automated applications. Driven by stepper or servo motors, it enables software-controlled Auto-Zoom and Auto-Focus, integrated into vision systems for rapid task switching.

• Linked Zoom: During continuous zoom, precision mechanical structures or electronic algorithms synchronously fine-tune the position of the focus lens group to maintain consistent focus, minimizing the need for repeated refocusing.

III. ZOOM LENSes in Machine Vision Inspection Applications

1. Multi-scale target detection: Within the same system, switching magnification allows both wide-field product positioning and counting, as well as high-resolution inspection of small-field product details (such as characters and scratches).

2. Long-distance high-precision measurement: At a fixed working distance, increasing magnification (telephoto end) enables accurate dimensional measurement of distant or hard-to-reach objects.

3. Detection of Minor Defects:

• Low magnification: Quickly scan the overall appearance of the product to detect obvious defects or assembly errors.
   
• High magnification: Conduct detailed inspections of specific areas (such as solder joints, chip pins, material surfaces) to identify minute cracks, bubbles, burrs, and other imperfections.