VCM vs T–Lens

Autofocus systems adjust the focus of a camera by changing the optical path between the lens and the image sensor. Two common approaches are Voice Coil Motor (VCM) based focusing and tunable lens (T-lens) technology. This paper describes how each technology works and outlines the main differences and tradeoffs. The discussion is based on publicly known principles and conversations with polight CEO Øyvind Isaksen.

Modern cameras require precise focus control. This is usually done by moving optical elements or by changing optical properties electronically. VCM and T-lens represent these two approaches.

A Voice Coil Motor uses an electromagnetic actuator to move lens elements along the optical axis. A current through a coil interacts with a magnetic field and creates a linear force. This force shifts the lens position to achieve focus. VCM systems are widely used in camera modules. They are compatible with many optical designs. The lens elements have physical mass, which introduces inertia. Power is required during movement and often to hold position.

A tunable lens changes focus by modifying the optical properties of the lens itself. This is typically done using MEMS or piezoelectric actuation. The lens shape or refractive index is adjusted electrically. No full lens translation is required. According to input from polight CEO Øyvind Isaksen, this approach reduces moving mass and allows fast and repeatable focus changes. Power consumption is generally low once focus is set.

VCM adjusts focus by mechanical movement. T-lens adjusts focus by optical modulation. VCM is a mature and cost-efficient solution. It works across a wide focus range. T-lens offers high precision and fast response. Integration can be more constrained by optical design and system requirements. Cost and availability differ depending on volume and application.

VCM and T-lens represent different design choices for autofocus systems. VCM relies on mechanical motion of lenses. T-lens relies on electrically controlled optics. The preferred solution depends on system size, power budget, response requirements, and integration constraints.