7. Understanding the Measurement Strategy
HDV systems can be operated with any of seven telecentric fixed-focus lenses with magnification from 0.14X to 4.0X and with 6.5:1 zoom optics with continuously adjustable magnification from 0.7X to 4.5X. With these lenses, magnification is the image size at the camera CCD detector divided by the object size. Since the CCD size is fixed (namely 9.93 x 8.70 mm), each magnification has a corresponding field of view (FOV), which is the CCD size divided by magnification. The higher the magnification, the higher the resolution but the smaller the field of view. The six telecentric optics with magnifications from 0.3X to 4.0X and the 6.5:1 zoom optics are mounted through a bayonet fitting and can be changed by the user in seconds. Note that the centering of the optical axis of different optics might vary by a small amount, so that all measurements on the same part need to be taken with the same optics. The larger 0.14X telecentric optics are not bayonet mounted. Instead, the optics are part of a dedicated machine.
7.1 Telecentric Lens Measurement Strategy
Select telecentric optics to perform high accuracy, high throughput FOV measurements. In general, select the largest lens whose field of view encompasses the entire part. The 0.14X lens accommodates parts up to 2.47 x 1.86 inches (63 x 47 mm). If the entire part cannot fit into the FOV, move the stage by up to 11.81 inches (300 mm) with the HDV300 or up to 15.75 inches (400 mm) with the HDV400, and the M3 software will seamlessly integrate FOV measurements with encoder readings from stage motion.
7.2 Zoom Optics Measurement Strategy
The 6.5:1 zoom optics allows magnification to be continuously adjusted from 0.7X to 4.5X. While the zoom optics can provide the same FOV as the four higher magnification telecentric lenses, the optics do not offer the same low optical distortion that is required for accurate FOV measurements. Select zoom optics to measure large parts which would not fit into a single FOV, also for smaller parts where extremely high magnification is required. The lowest magnification range accommodates parts up to 0.44 x 0.37 inches (11.2 x 9.4 mm) in the FOV. To measure large parts, locate the edge of interest at minimum magnification, then take the actual measurement at maximum magnification using the system's crosshairs. The parcentricity feature of the zoom optics ensures that a feature will remain at the optical center of the video image throughout the magnification range.
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