Stereo microscopy is a widely used low magnification optical technique for sample inspection, manipulation, measurement and documentation in many industrial applications. Many such microscopes provide continuous zoom magnification over a large range along with a 3-D view of the sample. For inspection and sample manipulation, these features are powerful tools but can also lead to error in measurement and documentation.
Here we will describe two potential problems which can arise when working with a stereo microscope, both leading to incorrect scaling of magnification. One is instrument reproducibility of the zoom setting and the other is human error where magnification setting is not properly transferred to the imaging system.

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Many Stereos provide a continuous zoom and / or a fixed magnification control knob. In using this knob, two things can happen: 1) the mechanical setting may not be reproducible and 2) the user may not realize the actual setting…by just simply forgetting to check it. In this case, one could reduce these risks by using a calibration standard each time prior to measurement. This step, however, can be time consuming and can potentially become another source of error.
To avoid this, recently introduced stereos microscopes have become more sophisticated with motor controlled zooms and integrated with the digital imaging systems, allowing connection between microscope settings and imaging software. This feature provides feedback from the microscope to the computer imaging system as to the precise zoom setting and also may allow the computer to set the zoom magnification to a pre-selected or previous settinginsuring reproducible measurement results with minimal interaction.

Tom Calahan
Product Manager / Materials Microscopy
Carl Zeiss MicroImaging, Inc.