The stereomicroscope is a light microscope that works with separate beam inputs and in this way creates a spatial impression in the sense of three-dimensionality. Stereomicroscopes correspond to either the Greenough or the Abbe type, with some additional special forms existing. In applied medicine, the devices are used in variations as slit lamps and colposcopes.
What is a stereomicroscope?
The stereomicroscope is a light microscope that uses separate beam inputs. Light microscopes image high magnifications of small structures and objects by exploiting optical effects. The stereomicroscope is a light microscope that provides a separate beam path for both eyes. When looking through the stereomicroscope, the eyes see the specimen from different angles for this reason. In this way, a kind of stereo effect is created, which produces a spatial impression of the image. The stereomicroscope is often called a binocular. In the true sense, however, it is to be distinguished from both the binocular and the stereo magnifier. Unlike magnifying glasses, the stereomicroscope has a magnification in two stages, which are provided by means of an objective and eyepiece. The stereomicroscope must also be distinguished from the binocular microscope, which corresponds to the conventional light microscope and works with two eyepiece views. Unlike the stereomicroscope, this light microscope works with only a single image of the specimen, which the integrated beam splitter on the eyepiece provides for both eyes. Despite first appearances, no 3D effects in the sense of additional image information are generated. The microscope must also be distinguished from the Leica/Wild Heerbrugg macroscope, which is similar in appearance to the stereomicroscope but corresponds to an incident light photomicroscope. Different forms of the stereo microscope exist. Among the best known microscope of this type is the Greenough-type microscope, invented by Horatio S. Greenough in the 19th century.
Forms, types and kinds
The Greenough-type stereomicroscope uses two fully separated beam paths. Two objectives in a common mount produce the stereo angle. The optical axes of the objectives are tilted a few degrees from each other. At a comparatively low price, this type of stereo microscope creates ideal imaging quality. However, additional equipment for microphotography or drawing tubes is difficult to attach. For this reason, the second type of stereomicroscope, the Abbe-type microscope, has been more popular in the meantime. The Abbe-Ty corresponds to a type of telescope invented by Ernst Abbe. The double objective of stereoscopy is missing in this model. It is replaced by a common main objective with a large diameter. The apertures behind the objective use only the edge rays at an angle of 11° to form the image, thus creating the stereo angle. A tube lens is located in front of the eyepiece. An integrated roller in the telescope system lets the user easily adjust the magnification. In addition to these two main types, there are several special forms of the stereo microscope. One example is the microscope base stereo, which corresponds to a small stereo microscope stand with an optics carrier. In addition to the main objective, the optics carrier carries a prism system that provides spatial separation of the incoming beams. A pocket binocular sits on top of the instrument. This type of microscope produces constant magnification to 12, 16 or 20 times.
Structure and operation
Stereo microscopes are used within teaching, research and engineering. Biology, medicine and dental technology offer the technique a particularly wide range of applications. The devices are used in these fields for preparative work, for example, or are used on ultramicrotomes. In medicine, the stereomicroscope is mainly used in a modified form and corresponds to a colposcope in this context. Inform of slit lamp microscopes also ophthalmology uses the devices. The surgical microscopes within surgery are more powerful than the stereomicroscope and only reproduce a reduced stereo effect. However, in the broadest sense, they can also be described as variations of the stereomicroscope. In addition to the medical field, stereomicroscopes are used in geology, paleontology, for material examinations or in mineralogy. Furthermore, the devices play a role in criminology and help with restoration work in the field of art.All stereo microscopes have a similar technique. Unlike the binocular microscope, they use two separate beam paths through which the observer sees the object from different angles, usually to directional differences of 11° to 16°. In this way, a spatial impression is created. The stereo angle created in this way is based on the convergence angle of the two eyes during near accommodation. A double iris diaphragm often sits in the tube ray path and increases depth of field.
Medical and health benefits
The stereomicroscope has a high medical and biological benefit. This benefit has been demonstrated at the latest Hand Spemann’s Nobel Prize in the category of biology, which he received for work in developmental physiology. The research would not have been possible without stereomicroscopy. In 1935, Spemann had documented the organizer effect within embryonic development and proved through transplantation experiments that tissues behave with site specificity. Apart from medical research, the stereomicroscope is also relevant to some extent in applied medicine in modified forms, primarily as a colposcope, slit lamp microscope and surgical microscope. In gynecological colposcopy, critical changes in the area of the cervix and cervical mucosa can be detected as part of the screening examination, such as small tissue defects, tumors and microhemorrhages. Ophthalmic slit lamps, on the other hand, can document the anterior, middle, and posterior segments of the eye, all the way to the retinal periphery, using a variety of exposure methods and light slit widths. Surgical microscopes are also standard in medicine today and have almost completely replaced surgical loupes. Compared with magnifying glasses, they offer higher magnification, quieter surgical fields, and much better illumination.
