Stereo microscope

A stereomicroscope is a special light microscope, wherein for both eyes, a separate optical path is provided. Both eyes see the specimen, therefore, from a slightly different angle, so that a " stereo effect ", ie a spatial impression of image quality occurs.

Stereo microscopes typically operate at magnifications below 100:1, because at high magnifications due to the rapidly decreasing depth only at these relatively low magnifications a spatial image is useful.

Accruals

In the laboratory jargon the stereomicroscope is often incorrectly referred to as binocular, sometimes stereo microscope. However, in contrast to a magnifying glass, a stereo microscope having a magnification by two-stage lens and the eyepiece.

Not to be confused is the stereo microscope with binocular microscope, so an ordinary light microscope with two Okulareinblicken. Here a single image of the specimen is exposed through a beam splitter in front of the eyepiece for comfortable observation for both eyes. Additional image information ( 3D effect ) are thus not achieved, it merely allows fatigue- free working.

Areas of application

Stereo microscopes are used in many areas of teaching, research and technology, but also for leisure activities:

In biology, medicine and dental technology it finds many applications. It is used for preparative work, and can, inter alia, also be used to ultramicrotomes. The Nobel Prize in biology for developmental physiology works by Hans Spemann was only made possible through the stereo microscope. In medicine, the stereo microscope is used in a slightly modified form as a colposcope, in gynecology, and as a slit lamp microscope for ophthalmology. The typical surgical microscopes surgery are slightly more modified by a mostly existing second observation equipment and a larger free working distance at the expense of weaker now much stereo effect.

Applications are also geology, paleontology, mineralogy, and materials testing as well as production of various kinds In geology are like stereo microscopes used because of the large manageable object field instead of conventional microscopes for the study of large-scale rock thin sections. For manufacturing and quality control of precision mechanical and electronic industrial stereo microscopes are used, where they are also attached to machines to monitor manufacturing processes. It is also important in forensics for the forensics, as well as for restoration work in archeology and art.

Technology

In contrast to a binocular microscope, there are two completely separate light paths through which the object is seen from two to 11 ° to 16 ° different directions at a stereomicroscope. This allows a spatial impression. This stereo angle corresponds to the angle of convergence of both eyes at Nahakkommodation (in the " distinct vision " at 25 cm). Sometimes a double iris diaphragm is turned on in the tube optical path or can be used in the devices of the telescope type with its own intermediate tube in addition to the infinite beam. It is used to increase the depth of field ( = axial resolution), especially in photomicrography, but stopping down at the expense of the ( lateral ) resolution capability. Are the photos but - as it is today often practiced - by a corresponding image processing program stacked, then the double iris diaphragm is superfluous.

Greenough - type

On the stereo microscopes, two different design principles apply. The older building type, the Greenough microscope, which was first made ​​at the suggestion of the American entomologists Horatio S. Greenough in 1892 by Carl Zeiss in Jena. In this type, both beam paths are constructively completely separated. The stereo angle is generated by two located in a common text, lenses, whose optical axes are inclined at about 14 ° to each other. The advantages of this type of equipment, a lower price and a better picture quality. The disadvantage is the difficult installation of additional equipment for coaxial, micro photography and drawing tubes. Therefore, the Greenough microscope has now been greatly displaced by the second subsequent building type; but it is increasingly produced again in recent times. Often have the modern Greenough microscopes already a built interface for the attachment of a camera. Microscopic drawing is using a Zeichenokulares ( place of the characters between the telescope tube type stereo microscopes) possible.

Abbe - type

The second building type is the type of telescope, which goes back to Ernst Abbe. It was first realized in the stereomicroscope SM XX " Citoplast " Carl Zeiss Jena, which was developed in 1936 in Jena, but only in 1946 after the reconstruction of the factory after the war could go into series production. The Dual Lens is absent in the telescope or Abbe type, instead there is a common main objective of large diameter. The stereo angle is here produced in that means panels behind the main lens to be used for image formation only the marginal rays which pass through the lens at an angle of 11 °. The intermediate image is located at an infinite distance. Therefore, an additional tube lens in front of the eyepiece is needed. The advantages of this design principle are:

( There is a Galilean or Dutch telescope from a converging and a diverging section. Meanwhile, both at the Greenough as well as the operating according to the telescope system stereo microscopes pancratic "Zoom" systems become widespread. , You are primarily designed for live observation of small animals suitable that should not come out of the field of view at the magnification change. systems are usually quite sufficient for other applications with fixed magnification levels, since the graduation of the magnification changer is fine enough. )

The disadvantages of the telescope principle, however, are:

However, some manufacturers ( Zeiss Göttingen) also offered for stereo microscopes type of telescope to special double lenses that could be mounted in place of the common main objective. This made it possible to take advantage of the Greenough - type in terms of image quality and on devices of the telescope type. Another way to increase the image quality of at least the microphotograph, provides a displacement of the main lens to the side of the photo- beam path until the optical axis of the main lens coincides with that of the photo- beam path. Wherein the beams are used for image formation near the optical axis, as in a macroscope (see below) or as the Greenough microscope, and thus minimizes the aberrations. This is achieved in by a sliding version, which is inserted between the main lens and the microscope body in parallel Unendlichstrahlengnag (eg Wild / Leica, Askania ).

Special shapes

An interesting special edition introduced the " microscope - based stereo " by Zeiss Oberkochen dar. It is a small stereo microscope stand with an optical carrier which includes a main lens and a prism system for the spatial separation of the beam paths. Completing it is through a special pocket binoculars. Together, this results in a small lightweight stereo microscope with constant magnification (12 -, 16 - or 20 -fold, depending on the used binoculars ) for travel and biological and paleontological field work.

A macroscope Leica / Wild Heerbrugg looks outwardly very similar to a stereo microscope. Here, however, there is a special incident light photomicroscope for lower magnification ranges. It is designed to image errors which are inevitable in the photograph by a stereomicroscope, and off. The Macroscope is indeed equipped with two eyepieces and an image inversion and corresponds in terms of the magnification range of a stereomicroscope. However, it does not generate a spatial image and is therefore only for photography, but not necessary for preparative work. These devices are usually priced considerably higher than expensive stereo microscopes of the telescope type.

Lighting and Accessories

In the stereo microscopy, the objects are usually illuminated from above, but is also often a transmitted light illumination built into the stand base or as an additional device, such as for the study of biological objects. In more modern facilities, a transmitted light dark field illumination. It can also be mixed with light from above and below to work. Recesses in objects (such bores in workpieces to be tested ) of the telescopic type can be illuminated by means of a coaxial illumination in microscopes. For a shadow-free illumination ring lights are available, which are clamped to the main objective.

For developmental physiological studies often a UV light source is used. Optionally, get one or more remote cold light lamps ( spotlights ) are used.

For the investigation of large area thin rock sections in geology there is attachable polarization analyzer and rotary tables with retractable auxiliary objects ( wave plate ). The analyzer is clamped down in front of the front lens of the objective.

For preparative work in biology many different interchangeable tripod types are available, for example Freiarmstative to study larger objects.

Manufacturer

In Germany and Switzerland, Leica Microsystems ( predecessor companies: Leitz and Wild Heerbrugg ) are stereo microscopes, among others, by Bresser, Carl Zeiss, Askania microscope technique Rathenow (formerly Kombinat Carl Zeiss Jena ) was prepared and capes. In Japan, stereo microscopes are manufactured, among others, Nikon and Olympus.