The focusing principle of camera modules is achieved by precisely controlling the distance between the lens and the image sensor, allowing light to focus accurately on the photosensitive element. The core mechanism can be divided into the following three levels of implementation:
01
Optical Physics Basics
Driven by the Gaussian Imaging FormulaAccording to the optical formula 1/u + 1/v = 1/f (where u is the object distance, v is the image distance, and f is the focal length), when the object distance changes, the image distance v must be dynamically adjusted to maintain image clarity. For example, when photographing distant objects, the object distance u increases, necessitating a reduction in the distance between the lens and the sensor v.
Defocus Detection Principle
When not accurately focused, light converges in front of or behind the sensor, resulting in a blurry image;
Ideal focus requires that light forms the smallest circle of confusion on the sensor surface.
02
Focusing Technology Implementation
1. Drive Mechanisms
|
Motor Type |
Working Principle |
Application Scenarios |
|
Voice Coil Motor （VCM） |
Current passing through the coil generates a magnetic field, interacting with a permanent magnet to drive lens displacement (stroke 250–400μm) |
Mobile phone cameras Compact modules |
|
Stepper Motor |
The gear/screw converts motor rotation into linear motion of the lens, high precision but slow response |
Industrial cameras Security lenses |
|
Piezoelectric Motor |
Utilizes voltage-induced deformation of piezoelectric ceramics to drive the lens, noiseless and low power consumption |
Medical endoscopes Precision instruments |
2. Detection Methods
Phase Detection (PDAF)Divides light through microlenses, calculating the phase difference between left and right to directly obtain the defocus amount, achieving millisecond-level focusing (e.g., mobile phone focusing < 0.3 seconds).
Contrast Detection (CDAF)Analyzes image edge contrast, gradually searching for the peak contrast position, slow speed but high accuracy.
Laser/TOF Distance MeasurementInfrared laser measures object distance, providing initial position reference for lens movement.
03
Typical Applications and Performance Adaptation
|
Scene |
Technical Solution |
Performance Indicators |
|
Mobile Photography |
VCM Motor + PDAF + Multi-frame Optimization |
Focusing speed ≤ 0.25 seconds Stroke 400μm |
|
Security Monitoring |
Stepper Motor + Electric Focusing + Wide Dynamic Exposure |
Focal length range 2.8–12mm Supports rain and fog penetration |
|
Medical Imaging |
Piezoelectric Motor + Contrast Detection + Macro Optics |
Displacement accuracy ±1μm, no electromagnetic interference |
|
Industrial Inspection |
High-rigidity Guide Rail + Global Shutter + Real-time Closed-loop |
Vibration resistant, repeat positioning Error < 2μm |
The core of the focusing system lies in the dynamic matching of object-image relationships, achieving precise capture from macro scenes to micron-level structures through optomechanical-electrical collaboration. Future trends will integrate AI predictive focusing and multi-sensor fusion (such as depth + spectrum), breaking through the limitations of complex environments.
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