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Dr Spyros Efthymiou, of Optotune, and Jools Hudson, of Gardasoft, on liquid lens technology


While traditional optical systems enable focusing within certain limits according to the required distance, one or more lenses must be moved along the optical axis to achieve this. Tis requires motors and mechanical guides, which limit not only the overall size and the response time, but also restrict the robustness and service life of any solution. Variable focal length lenses provide an


interesting alternative for such applications. Te technical basis of this is the variable curvature of a lens consisting of a membrane filled with fluid. If the pressure within the lens is altered, the curvature can be adjusted. A change to the lens radius of a few micrometres can achieve the same optical effect as the mechanical displacement of a lens by several centimetres. Optical systems can thus be designed to be more compact, oſten with fewer lenses and without any translational movement. Focusing can be achieved in just a few


milliseconds by the application of current, removing the need for manual or motorised refocusing for imaging objects of different heights. Tis can best be seen in the example of a system for reading addresses on packages: the heights of such packages can vary continuously. Under these circumstances in order to capture the desired information in focus, the working distance to the vision system or the focus of the optics would have to be adjusted for each package, which oſten is not achievable with the necessary speed using mechanical means. Te electrically tuneable lenses offer a wide


range of optical power and thus the possibility to focus on objects at a wide range of working distances, and within milliseconds. A liquid lens solution is also very compact and can even be integrated in handheld devices. Without relying on any moving parts, millions or even billions of cycles are specified, significantly increasing the time before failure compared to alternative solutions. In addition, when compared to other solutions, the tuneable lens is definitely cost- effective, especially when the use of multiple camera systems can be avoided. Liquid lenses can be combined with


conventional lenses and mounted either between www.imveurope.com @imveurope


In addition to Basler’s original equipment lenses covering a resolution of 5 megapixels for sensors smaller than 1/2 inch, Basler now also offers lenses for sensors up to 2/3 inch. The 2/3-inch lenses are suitable for sensors with a resolution of up to 2 megapixels, and are ideal for applications where low resolutions are sufficient.


Gardasoft’s TR-CL series of industrial lens controllers


the solid lens and the camera for macro imaging, or in front of the solid lens for longer working distances. A 200mm macro lens combined with a liquid lens will typically allow the focus to be adjusted between 100mm and infinity. As well as applications for imaging products of


Liquid lenses are ideal for focusing on objects that aren’t flat


different sizes, liquid lenses are ideal for focusing on objects that aren’t flat or inspecting features at different heights. Multiple focal points and rapid refocusing can also reduce the number of cameras required for the installation. Fixed focus lenses have a working range that is limited by the depth of field. Increasing the depth of field requires the aperture to be stopped down, which reduces the amount of light reaching the image sensor. Liquid lenses avoid this problem and can allow the system to operate at lower light levels.


Te Optotune EL-16-40 is one of the world’s


largest electrically focused lenses, with a clear aperture of 16mm; it can operate as either a convex or concave lens. Stemmer Imaging also supplies Gardasoſt’s TR-CL series of industrial lens controllers, which have been developed specifically to control Optotune liquid lenses by means of a constant current drive. Te Gardasoſt TR-CL lens controller allows


macro changes in lens settings to be completed in less than 10ms with accurate and repeatable focus and full temperature compensation. Te TR-CL is fully GigE Vision compliant, so that any GigE Vision client image processing soſtware, such as Cognex’s VisionPro or Stemmer Imaging’s CVB, can be used to view the lens properties and modify the lens controller settings. www.optotune.com www.gardasoft.com


The C-mount lenses are optimised for use with Basler Ace, Dart and Pulse cameras with sensors between 1/2 inch and 2/3 inch, and have an excellent price/performance ratio. The lenses are available in six different focal lengths (8mm, 12mm, 15mm, 25mm, 35mm, and 50mm) and can be used in the visible wavelength range of 400nm to 700nm. www.baslerweb.com


Edmund Optics has rebranded its imaging filters as Techspec machine vision filters to address their primary use with the company’s


machine vision cameras and lenses. Designed for demanding machine vision and imaging applications, the filters pass or block specific UV, visible or IR wavelengths and provide wide angles of incidence for maximum versatility. The filters are very durable thanks to their hard


coating, and offer a high and flat transmission profile to provide even illumination. They exhibit sharp cut-on and cut-off wavelengths and optimal signal-to-noise ratio in imaging systems without losing light intensity. www.edmundoptics.eu


Kowa has launched a lens series for Intelligent Transportation Systems (ITS). The JC5M-IR series is suitable for


cameras with up to 2/3 inch chip size. The new C-mount ITS lenses are IR-corrected, in that they minimise the focus shift when switching from visible light to infrared illumination for night surveillance.


The lens series has a manual iris. It is ideally suited for sensors with a pixel size of 3.45μm, such as the Sony IMX250 and IMX252. The series is available with the focal lengths of 16mm, 25mm and 35mm, the usual focal lengths for traffic monitoring. www.kowa-lenses.com


December 2017/January 2018 • Imaging and Machine Vision Europe 35


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