Monday, May 2, 2016

Understanding Stereo Microscope Optics

There are two types of optical designs for stereo microscopes.
Each stereo microscope system has its advantages. Specifically, with the CMO system (a), because of the optical design, there is a capacity for much higher magnification and resolution. This design is most commonly used in research applications requiring both higher magnification and higher resolution (NA). This design results in a relatively flat field and does not generate a pronounced three dimensional image.

For the Greenough system, the primary advantage is that it provides a pronounced three dimensional image and is very useful for relatively low magnification and inspection of items with "depth". Because of the "V" design of the optical path (b), as magnification is increased, both by the use of auxiliary lenses and higher magnification eyepieces, there is a divergence of the point on the subject where each optical path is focused and resolution appears to degrade. This is what limits the effective magnification range of this design to approximately 125x.

Stereo microscope CMO versus greenough optical design.
(a) CMO optical design (b) Greenough optical design

The images below were captured from the left and right eyetubes on a Greenough stereo microscope. As you can see, the crossline in the left image is offset to the left, and the crossline in the right image is offset to the right. Everything is exactly the same for these two images except for the moving camera from the left to the right eyetube. Specifically, this is exactly what a Greenough system should look like, because this is how the microscope system generates a three dimensional type of image.

Greenough stereo microscope versus CMO stereo microscope.
Greenough Stereo Microscope image from left eyetube and right eyetube.

If you have questions about which stereo microscope system will best meet your needs please contact Microscope World.