The TEC-V7X lens from Computar, now available from Stemmer Imaging, offers dual functionality. Designed for use with high resolution cameras up to 5 Megapixels with 1/1.1-inch image sensors, this versatile lens operates both as a 7x macro zoom lens with 0.07x to 0.5x magnification and as a telecentric lens within the 0.25x to 0.5x magnification range. It provides excellent brightness throughout the zoom range, maintaining 70 per cent illumination at both centre and corners.
The low distortion property of the telecentric lens makes it perfect for applications such as silicon wafer alignment, print registration and the measurement of many different types of 2D objects. Because light is collimated as it enters the lens, images of identical objects are imaged with the same magnification, even if they are at different distances from the lens. This magnification invariance eliminates the accuracy and repeatability problems in applications where measurements need to be made but the exact distance between the lens and the object is unknown. The working distance of the TEC-V7X is adjustable from 182-577mm and a F4.3-32C manual iris allows precise control of depth of field and contrast.
The constant magnification properties offered by the telecentric lens mean that it is also ideally suited to making measurements in applications where the object(s) being imaged have no natural rest position, such as in optical fibre or manufacture, where the wire or fibre can vibrate or oscillate as it passes the lens at high speed. Since the distance from the wire to the lens is continuously changing, a standard lens would produce images with varying apparent width or gauge of the wire. However the telecentric lens produces an image in which the width of the wire is constant no matter how far the wire is from the lens, making it easy to monitor accurately any changes in the width that are genuinely due to variations in the production process.
