The technology is based on the principle of a shape-changing lens. Consisting of a container filled with optical fluid and then sealed off with an elastic polymer membrane. When an electromagnetic actuator is used to exert pressure on the container holding the fluid, a deflection of the lens occurs. The resulting effect is the focal length of the lens is then controlled by the current flowing through the coil of the actuator. The relationship between the current and the optical power, which in the inverse of focal length, is linear.
Tunable lenses are designed to deflect in a positive direction, which means that the actuator pushes towards the membrane. In early development, to achieve negative optical power, a plano-concave offset lens was added. Today’s tunable lenses now have the actuator bonded to the membrane and is able to pull the membrane away from the container with negative currents, which result in a concave lens shape.
The membrane thickness influences the tuning range of the lens, thinner membranes, achieve a larger range of optical power due to the reduced restoring force. The refractive power of the lens can be changed by using different optical fluids with different indexes of of refraction.
For machine vision applications the benefits of using liquid tunable lenses are:
- Greater working distance
- Faster response
- Reduced lighting requirements
- Easy to install and use
Optotune, based in Switzerland, recommends using a tunable lens in 3 configurations:
- Front- Lens, mounted on filter thread of a fixed focus lens you can achieve working distances from infinity to 100mm. This is the most versatile configuration.
- Back-Lens configuration – the tunable now lens acts as a distance ring when placed between the caemra and a fixed focus lens, providing an easy mechanical solution. This configuration will provide the best quality for short working distances.
- High magnification or Telecentric – here the tunable lens is placed between the tube lens and the zoom lens and is best for high magnification applications. This configuration works best with infinity corrected lenses and achieves up to 100x magnification.
Excellent applications for a front lens configuration is Bar Code reading, Robotic Vision, package sorting and bottle inspection. Back lens configuration is an excellent choice for C-mount macro imaging applications and works with lenses at a focal length >=35mm. Other applications for back lens configuration is Electronic inspection, laser processing, contact lens inspection and diamond inspection. High magnification/telecentric applications benefit from a tunable lens by increasing the Z-range and optimizing a telecentric lens for large format imaging. Recommended applications for this use of a tunable lens is in, camera phone lens inspection, IC inspection, LCD & PCB inspection and particle counting in liquids.
This is a high level over view of the technology and where it may best be applied. For more information on tunable lenses, or to discuss your application please give us a call at 813-984-0125 or email [email protected] You can also explore tunable lenses on our website at, Optotune lenses at PyramidImaging.com. Content courtesy of Optotune.