Top Tips for Non-contact Measurement Using Optical Microscopy

Optimise your non-contact measurement process using optical microscopy techniques for high precision and reproducibility. Learn how to achieve accurate, reliable measurements through proper calibration, advanced imaging methods, and consistent procedures.

1. Choose the Appropriate Magnification and Objective Lens

• Objective lens quality and magnification play a crucial role in optical measurements. Choose the magnification that provides sufficient resolution while maintaining the field of view required for the measurement.
• Use high numerical aperture (NA) objectives for improved resolution and image quality, especially for fine detail measurements.
• Avoid using the maximum magnification unless necessary, as it can reduce depth of field and make focusing more challenging.

2. Ensure Proper Illumination

• Köhler illumination is essential for uniform lighting across the sample. It improves contrast and minimises shadows, which can distort measurements.
• Use consistent lighting—whether it’s bright-field, dark-field, or differential interference contrast (DIC)—and ensure that the intensity and angle of illumination are consistent across all measurements.
• If you’re measuring transparent samples, consider phase contrast or DIC to enhance edge detection and improve measurement accuracy.

3. Focus Control and Depth of Field

• Ensure precise focus before taking measurements. In optical microscopy, a slight shift in focus can alter measurement results, particularly for height or thickness.
• Use motorised focusing systems when possible to ensure repeatable focus positioning, which is especially helpful in 3D optical microscopy techniques like confocal microscopy.
• Be mindful of the depth of field—as magnification increases, the depth of field decreases, making focus even more critical.

4. Minimise Lens Aberrations

• Chromatic and spherical aberrations can distort measurements. Ensure that the objective lenses are corrected for aberrations by using apochromatic or plan achromatic lenses, which improve edge sharpness and measurement accuracy.
• Use software-based image correction to compensate for minor aberrations.

5. Use Automated or Semi-automated Systems

• Automated image capture and measurement systems can significantly enhance the precision and repeatability of measurements.
• If you’re doing 3D measurements, consider using confocal or digital holographic microscopy, which provides detailed height information by capturing a series of images at different focal planes.
• The 3-axis Hawk Meaurement System offers full automated capability for innovative and accuracte non-contact measurement.

6. Edge Detection for Dimensional Measurement

• Use image processing techniques like edge detection algorithms to improve measurement accuracy. This is especially important for detecting the boundaries of the features being measured.
• Implement thresholding or grayscale level adjustments to define edges more clearly and avoid measurement bias due to poor edge contrast.
• Utilising the Swift Duo allows you to switch between video measuring for high contrast edges and optical measurement for lower contrast edges where more users can implement tresholds for repeatability where and when required.

7. Software and Digital Calibration

• Ensure that the microscope’s measurement software is correctly calibrated. Use a calibration grid or micrometer slide to calibrate the pixel-to-distance ratio in the software for each magnification setting.
• Regularly update and recalibrate the software to account for any potential drift in measurements over time.
• All non-contact measurement products supplied by Hawker Richardson and manufactured by Vision Engineering are initially calibrated using a grid from the NLEC for maximum traceability – find out more by watching this simple video to explain NLEC & SLEC Error Correction.

One of the key products which takes into consideration a lot of the tip mentioned above is the LVC 200 and 400 which are also manufactured by Vision Engineering.

If you have more questions, please speak to one of our engineers who will be delighted to help with your measurement requirements.

Click here to see all of the non-contact measurement solutions by Vision Engineering