Around 1890, the American biologist and zoologist Horatio S. Greenough introduced a design principle for optical instruments which is still used by all major manufacturers today [1-3]. Stereo microscopes based on the “Greenough principle” deliver genuine stereoscopic images of a very high quality. In the late 1950s, Bausch & Lomb, presented its StereoZoom® Greenough design with a groundbreaking innovation: a stepless magnification (zoom) changer . Almost all modern stereo microscope designs are based on a zoom system. In 1957, the American Optical Company introduced a stereo microscope with optics based on the telescope or CMO (Common Main Objective) principle . This type of stereo microscope was soon offered, in addition to the Greenough type, by all manufacturers due to its modularity and high performance.
A stereo microscope can be a big investment, therefore, the selection process should be taken very seriously. To get the most out of a microscope, users should ask themselves the following questions:
- Does it involve screening and sorting?
- Is any sample manipulation needed?
- Is documentation necessary?
- Is high resolution more important than long working distance or the other way around?
- When it comes to using the microscope for many hours, it is important to consider ergonomic accessories as they can prevent repetitive strain injuries.
- Depending on the number of different users, it is advisable to have a microscope which can be adjusted to the preference of each user.
- Modular solutions may look like a higher investment, but in the long run they will save money thanks to their versatility, ability to accommodate different users, and large variety of add-ons and accessories.
- Users who tend to work at the same magnification don’t require a large zoom range.
- If the workflow requires search, find, and sample manipulation, then it may be useful to have a large zoom range to go from low to high magnification.
- At the same zoom magnification, a bigger or smaller object field can be seen, depending on the eyepieces. A larger object field allows users to maintain a better orientation on the sample.
- A larger working distance means a greater distance between the top of the sample and the objective’s front lens, allowing for easier handling of the sample during use.
- Higher NA results in higher resolution, but usually reduced depth of field.
- The FusionOptics technology combines high resolution with more depth of field.
- Plan optics: Correction for image flatness over the entire object field which is useful for all applications.
- Achromat (achromatic) optics: For applications where true color reproduction is not important and mainly geometrical features are assessed.
- Apochromat (