Small form-factor VGA camera with variable focus by liquid lens

• Published in: SPIE Proceedings, Optics, Photonics, and Digital Technologies for Multimedia Applications
• Main Authors: Oikarinen, Kari, Aikio, Mika
• Format: Other Non-Article Part of Journal/Newspaper
• Language: English
• Published: International Society for Optics and Photonics SPIE 2010
• Subjects: adaptive optics; camera design; liquid lens; variable focus; Arctic
• Online Access: https://cris.vtt.fi/en/publications/5bc3312a-fe6b-410b-b1f7-8aa2b8a22c41; https://doi.org/10.1117/12.851142

We present the design of a 24 mm long variable focus lens for 1/4" sensor. The chosen CMOS color sensor has VGA (640×480) resolution and 5.6 μm pixel size. The lens utilizes one Varioptic Arctic 320 liquid lens that has a voltage-controllable focal length due to the electrowetting effect. There are no mechanical moving parts. The principle of operation of the liquid lens is explained briefly. We discuss designing optical systems with this type of lens. This includes a modeling approach that allows entering a voltage value to modify the configuration of the liquid lens. The presented design consists only of spherical glass surfaces. The choice to use spherical surfaces was made in order to decrease the costs of manufacturing and provide more predictable performance by the better established method. Fabrication tolerances are compensated by the adjustability of the liquid lens, further increasing the feasibility of manufacturing. The lens is manufactured and assembled into a demonstrator camera. It has an f-number of 2.5 and 40 degree full field of view. The effective focal length varies around 6 millimeters as the liquid lens is adjusted. In simulations we have achieved a focus distance controllable between 20 millimeters and infinity. The design differs from previous approaches by having the aperture stop in the middle of the system instead of in front.