History of the microscope

What is the best stereo microscope?

How to choose a stereo microscope that is right for you


There is a vast array of stereo microscopes available in the market place, so it can be difficult to decide on which one is the best stereo microscope for you. But in beginning your search, it is likely that you will consider the following questions:


  1. What magnification do I require?
  2. Do I need to 'do' anything to the sample whilst being magnified?
  3. Do I have any special requirements?
  4. What is my budget?

What magnification do I require?


1.   Stereo microscope magnifications can range from as little as 2x up to 300x, but typically might be between 20x and 80x, depending on what you are looking at, of course. A common mistake is to believe that you need a higher magnification than is actually required. For many applications, 4x - 20x is enough, though having the ability to go higher may be a desirable feature. As a guide, if you need to view a whole sample, your magnification requirement is likely to be quite low, perhaps no more than 10x. If you will be viewing small details then 40x may actually be more than enough, however up to 80x is also quite common.


Do I need to 'do' anything to the sample whilst being magnified?


2.   If you just need to 'do' something whilst your subject is being magnified, then this can affect your choice of stereo microscope. Different stereo microscopes will have surprisingly different optical specifications, resulting in different working distances (distance from the bottom of the objective lens to the point in sharp focus) and field of view (size of the whole field when looking through the eyepieces). If you are soldering a printed circuit board, it may be more important to have a long working distance, whereas if you are counting items, then a large field of view will be of great assistance.


Do I have any special requirements?


3.   A very open question, but if you need to capture images, or require special illumination (such as UV light), then naturally you need a stereo microscope that can offer these features.


What is my budget?


4.   Always an important consideration, but thankfully there is a vast array of choice, which I guess is half the problem! In helping make a final decision, it may is certainly helpful to appreciate the different optical designs of stereo microscope, which can have difference advantages and disadvantages, which we have not yet considered.


Fixed magnification stereo microscopes


Fixed magnification stereo microscopes the most basic stereo microscope, therefore being the least expensive (since there is no zoom mechanism). To change magnification, you will need to change the objective (magnification) lens, which typically might be 20x, 40x, 60x magnification etc. Many manipulation tasks can be performed at fixed magnification, so these stereo microscopes are entirely fit for purpose. However, in reality the equivalent stereo zoom microscopes are very inexpensive and with zoom capability are almost always preferred to fixed magnification systems. The illustrated microscope (courtesy of Celestron) has fixed magnifications of 20x and 40x.


Stereo microscopes - Greenough


Greenough-type stereo zoom microscopes provide excellent stereo imaging, high levels of magnification, plus a wide zoom range, making these units ideal for "workhorse" type applications, such as printed circuit board inspection, dissecting biological specimens, or similar routine tasks. The microscopes are relatively small, inexpensive, very rugged, simple to use, and easy to maintain. Certain accessories, such as a trinocular head (for image capture) are available, but need to specified at the time of purchase, so are less flexible than the CMO modular design. The illustrated stereo microscope (courtesy of Vision Engineering) has a zoom ratio of 6.3:1 with a standard zoom range of 8x - 50x and a maximum magnification of 200x.


Stereo microscope with Common Main Objective (CMO)


Stereo microscopes (of the CMO optical design) may often cost several times more than a Greenough stereo microscope, but are generally used for more complex applications requiring high resolution and/or advanced accessories. The optical design of CMO stereo microscopes lends themselves perfectly to a modular construction, permitting the addition of many different optical and illumination accessories, at a later date if required. The extra cost of CMO systems is therefore easier to justify with greater flexibility and arguably superior optics. The illustrated stereo microscope (courtesy of Vision Engineering) has a zoom ratio of 10:1 with a standard zoom range of 8x - 80x and a maximum magnification of 320x.


A few final notes


In general CMO stereo microscopes have a greater light-gathering power than the Greenough-type design and are often more highly corrected for optical aberration, though in most circumstances, the choice between Greenough or CMO stereo microscopes is usually based on the application, rather than whether one design is superior to the other.


Greenough stereo microscopes are typically employed for "workhorse" applications, such as printed circuit board inspection, dissecting biological specimens, or similar routine tasks. These microscopes are relatively small, inexpensive, very rugged, simple to use, and easy to maintain.


CMO stereo microscopes are generally used for more complex applications requiring high resolution with advanced optical and illumination accessories. The wide spectrum of accessories available for these microscopes lends to their strength in these areas.


However, often a major consideration is cost. CMO stereo microscopes can cost several times more than a Greenough stereo microscope, so this naturally will strongly influence buying decisions.

Microscope History