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Marc Silverstein

Metrology

Under the Stereo Microscope

The benefits of stereo optics in production scenarios

Published: Tuesday, April 19, 2016 - 15:48

Every day, new technology creates smaller and smaller materials and components. In many industries these parts require high magnification, sometimes up to 1,000X, to see submicron features. This is accomplished using a compound or upright microscope, where the user can select the objective lens. But in many applications, a stereo microscope might be a better choice.

Why would you need a stereo microscope? Many times we’re looking at objects or features that are millimeters in size and have surface topography. In these cases, a magnification of 10X–50X is more than enough to do the job, and that’s where stereo microscopes offer many benefits over a compound microscope.

Galilean optics

Let’s first look at the stereo aspect. We all know that our brains interpret three dimensions by using our two eyes and processing the differences between what each eye sees. Why would you want to give this up? Many stereo microscopes utilize Galilean optics (figure 1), i.e., two independent and parallel optical paths that are focused through a single objective to a focal point on your sample. This provides the same different angle to each eye, and thus the same stereo effect.


Figure 1: Galilean optics as seen in the Olympus SZX7 stereo microscope

Why is this so important? When working under the microscope, our hand-eye coordination critically needs that three-dimensional depth for us to put our hands and tools in the correct location. We see this significantly in the world of medical device manufacturers. In that industry, production areas with 25 or more personnel use stereo microscopes to assemble and adjust products that help keep us alive. Products like pacemakers and artificial heart valves require that hands-on touch for perfect construction, but our eyes are the weak point. Stereo microscopes make up that difference.

We also see this in electronics and many other fields. In electronics, many operators solder small electrical connections that are close together and could easily short to each other, so magnification and depth are critical here as well.

Larger working distances enable viewing of bigger samples

Another advantage of stereo microscopes is the large working distances. Working distance is how far your sample is from the objective lens when properly in focus. With fairly large components, it’s nice to have three to four inches of space between the lens and your sample. This distance does vary by the objective magnification, but a working distance of more than six inches can be achieved provided the magnification is within your needs. This working distance also helps when trying to look into a void. In that instance, the area in focus might be a few inches inside the sample, but the top of the sample would not impact your objective lens.

One more example of when a stereo microscope is ideal is for detailed inspection of large components. We see this with welds in the automotive industry. Welds in car body panels occur in many locations, and how well these welds hold up is discovered in the details. Samples are taken from the production line and cross-sectioned through the weld. Looking at how far the weld penetrates into the metal is one aspect, but tiny voids in the weld itself can show the potential for a future stress failure.

A versatile, ergonomic observation solution

Many other aspects make working under a stereo microscope the correct choice for the job. Numerous ergonomic improvements have been made (figure 2), allowing for reduced stress and better posture while working at the microscope for several hours. LED lighting can provide brighter illumination with less heat and longer bulb life. Various microscope stand options (figure 3) allow you to mount your microscope in unlimited variations to look at your sample from any angle.

Conclusion

If your inspection needs allow working at lower magnifications, a stereo microscope might be a better choice than a compound microscope. Along with a larger field-of-view and longer working distance, a stereo microscope also provides a 3D view of your work, which is important if you have to physically touch the sample. All of these aspects make working under a stereo microscope a great solution for your observation needs.


Figure 2: Ergonomic enhancements to stereo microscopes allow proper posture and comfortable viewing for extended periods of time.


Figure 3: Versatile microscope stands allow a stereo microscope to be mounted in unlimited positions.

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About The Author

Marc Silverstein’s picture

Marc Silverstein

Marc Silverstein is the product manager of optical metrology hardware and software at Olympus Scientific Solutions America. Silverstein manages core industrial microscopes and stream metrology software activities from feature development to launch.