Differences between CMO and Greenough Stereomicroscopes

In this article, we'll explore how CMO (Common Main Objective) and Greenough Stereomicroscopes differ in their optical setups. These differences affect various optical properties, leading to advantages and disadvantages for each system when compared to the other.

The main difference is the light path

• The main difference in the optical design is the light path - In the Greenough stereomicroscope, the light path is at a fixed angle typically between 10 to 20 degrees.
• In the CMO stereomicroscope, the light travels in a straight parallel line, when it passes through the objective lens, it gets slightly angled. This adjustment enables the creation of a stereo image.
• The straight light path in CMO stereomicroscopes offers versatility in configuring optical modules within the optical systems, including options like coaxial light, ergonomic optical modules, integrated cameras, and more.

The main properties of each stereomicroscope

illumination

• Greenough - Reflected light using a ring light, spotlight (goosenecks), and near vertical light. Transmitted light using illumination beneath the sample.
• CMO - Reflected light using a ring light, spotlight (goosenecks), coaxial light (light that goes through the main objective), fluorescence light, and near vertical light. Transmitted light using illumination beneath the sample.

Magnification

• Greenough - Max magnification of 110x (without empty magnification).?
• CMO - Max magnification of 320x (without empty magnification)

Resolution (lp - line pairs)

• Greenough - Max resolution of 500 lp/mm.
• CMO - Max resolution of 1050 lp/mm.

Death Of Field (DOF)

• Greenough - Very high depth of field value. Greenough stereomicroscopes are more suited for large 3D objects than CMO stereomicroscopes.
• CMO - Medium depth of field value. CMO stereomicroscopes are more suited for small 3D objects or flat samples.

Field OF View (FOV)

• Greenough - Large field of view 0.6 mm - 75.4 mm.
• CMO - Large field of view 0.19 mm - 116.8 mm.

Working Distance (WD)

• Greenough - Large working distance of 200 mm.
• CMO - Very Large working distance of 300 mm.

The trade-off between working distance and magnification

The trade-off in stereomicroscopes involves balancing magnification and working distance. Higher magnification often means a shorter working distance and better resolution, requiring the microscope to be closer to the specimen for clear imaging, while lower magnification provides a greater working distance and field of view but sacrifices detail. Example in the following image.

CMO vs. Greenough Stereomicroscopes Summary