The 100x oil immersion objective often ends up being underutilised. The extra effort required for sample preparation and cleaning means the 100x objective is used much less frequently than expected. A 60x microscope objective also shows many details with a greater depth of field and does not require immersion. In combination with a 15x eyepiece, a magnification of 900x can be easily achieved.
2) Auxiliary Lenses or Additional/Interchangeable Objectives for Stereo Microscopes
With stereo microscopes featuring zoom objectives, the magnification can be adjusted with auxiliary lenses. These so-called Barlow lenses or Shapley lenses are screwed onto the objective mount. They are available with factors ranging from 0.5x to 2.0x (depending on the model). Magnification can thus be increased or decreased. This is helpful, for example, when examining larger objects such as components, electronics, or insects.
An important additional effect: auxiliary lenses alter the working distance and depth of field. A factor of less than 1.0x increases the working distance and depth of field, which is particularly useful when working (e.g., dissecting, soldering).
It can be beneficial to choose an optical configuration that shows fewer details but has a greater depth of field when working under the microscope. This is achieved by using a lower objective magnification combined with higher magnification eyepieces. For example, with the BRESSER Biorit ICD-CS 5802530, 10x magnification can be achieved in two different ways:
0.5x objective, 20x eyepiece pair
1.0x objective, 10x eyepiece pair
The first combination offers more working distance and depth of field than the second, while the second combination shows finer details.
3) Additional Microscope Eyepieces
The maximum possible (beneficial) magnification, resulting from the combination of objective and eyepiece magnification, is higher for all microscopes than what can be achieved with a 10x eyepiece. The objective shows finer details than can be seen with a 10x microscope eyepiece. Much more can be achieved!
The rule of thumb is:
Numerical Aperture of the objective x 1000 = beneficial magnificationg
The numerical aperture (NA) is often printed on the microscope objective. According to the rule of thumb above, a simple 40x objective with NA 0.6 can achieve a magnification of 600x without quality loss. For this, a 15x eyepiece is needed instead of the supplied 10x eyepiece.
For stereo microscope objectives, it is uncommon to specify the numerical aperture. However, at low magnifications, it is relatively higher than at high magnifications. This means that even 20x or 25x eyepieces can be effectively used with stereo microscopes. In this way, depending on the model, magnifications in the range of 50x-100x can also be achieved with stereo microscopes – maintaining high depth of field and large working distance.
Therefore, it makes sense to consider upgrading your microscope depending on its application. Using a microscope with well-matched magnification is much more enjoyable, ergonomic, and leads to better results.
Glossary:
Achromat: a multi-lens objective that reduces chromatic aberration. The image field is curved, meaning some refocusing is needed between the centre and the edge of the image.Planachromat: a multi-lens system with plan correction. Both the centre and the edge of the image are in focus simultaneously; particularly important in photography.
Infinity optics: a system where the objective forms an image “at infinity”. The real image is made visible only through an additional tube lens. The advantage is that the distance between the objective and the eyepiece/camera can be varied, allowing additional components (filter sliders, incident light systems, polariser/analysers) to be easily integrated or removed from the optical system. The opposite is finite optics (160).
Numerical Aperture (NA): a value specific to the objective that describes its resolving power. The higher the NA, the finer the details that can be resolved. The angle of the light cone entering the front lens of the objective (aperture angle) is crucial for this. The light cone must be appropriately shaped by the condenser or condenser diaphragm for the objective to achieve its maximum resolution. Therefore, an NA is not only printed on the objective but also on the condenser. Values greater than 0.9 usually require (oil) immersion.
The numerical aperture can be compared to the f-number (aperture) in photography. Stopping down the objective to increase depth of field and contrast (but decreasing detail resolution) in microscopy is not done at the objective itself but using the condenser diaphragm.
