(MIC) Stereoscopic Microscope Lesson

Stereoscopic Microscope

A stereoscopic microscope views particles of evidence in three dimensions and allows the investigator to turn over a tiny object such as a seed or a hair beneath the microscope. When using a stereoscopic microscope, the light is reflected from the surface of the specimen rather than through the specimen as the compound microscope does. This is especially useful when the specimen for analysis is too dense or thick for the light to properly transmit. Unlike the compound microscope, the image formed on a stereoscopic microscope is viewed in the original orientation rather than "upside down and backwards".

While modern stereo microscopes were developed in the recent past, an early version of the stereo microscope was actually created in 1671. The inventor was a Capuchin Franciscan monk named Cherubin d'Orleans. He developed a device that is now called a "Pseudoscope" in which a person looks through a set of binocular lenses with a separate eyepiece for each eye. The images from each eyepiece are viewed by the opposite side eye. To clarify, the image from the right lens was viewed by the left eye, while the image from the left lens was viewed by the right eye. The image appears to the viewer to be in 3D, but it is actually inverted vertically. For example, if one viewed a box on the floor using the pseudoscope, it would actually look like a box shaped hole in the floor rather than a box sitting on the floor. While this may seem odd, it was a great scientific discovery because it led to exciting new ideas in the fields of physics and human vision. The modern stereoscopic microscope was later developed and refined through a series of stereoscopic viewing devices that were popular in the 1800s. The stereoscopic microscope design developed by Horatio Greenough is often considered the first true stereo microscope that delivered true three dimensional views. Rather than reversing the eyepieces as the pseudoscope had, each eyepiece viewed the image on the corresponding side of the specimen. The Greenough design incorporated two special prisms, known as Porro Prisms, inside the microscope which afforded the correct optical pathways to view the images in stereo-vision, or 3D. The image of the item being examined is in 3D due to the placement of the two eyepieces at different angles. The brain receives and interprets the images from the two differently angled eyepieces and pieces them together into a 3D rendering of the image. The Greenough design was developed and presented to the Carl Zeiss company by Horatio Greenough in the late 1800s and was first commercially produced in 1897. Zeiss still produces Greenough design stereoscopic microscopes more than 100 years later!

Stereoscopic microscopes are often used in Forensic Science because of their versatility in viewing evidence of larger or irregular size. While a stereoscopic microscope does not offer the higher magnification found in other types of microscopes, it does allow samples that would not normally fit under a conventional microscope to be viewed microscopically. It is also used in cases with live animals or organisms being dissected, such as in entomology, because the specimens can be rotated, manipulated and viewed freely without being mounted on slides. These microscopes are often used on the majority of trace evidence before being examined in other more intrusive manners. This is because the stereoscopic microscope allows for observation and analysis without damaging or corrupting the integrity of the evidence. The evidence is observed under the stereoscopic microscope to identify any distinguishing marks or other observations and then is often sent for further analytical procedures which are more intrusive.

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