Reflected light microscopy
The reflected light microscopy is a method of microscopy .
In contrast to the transmitted light microscope , the observed sample is not irradiated with incident light microscopy. In the light microscope, the sample is from the direction of objective , often through the lens itself, illuminated . This article is about incident light microscopy with normal white light. Fluorescence microscopy , which also mostly uses reflected light, is described in a separate article.
As with transmitted light microscopy, there are also two different construction approaches for incident light microscopy: the upright and the inverse (or also inverted) construction. The Köhler lighting is common to both construction methods .
Upright reflected light microscopes have a similar structure to typical transmitted light microscopes, but usually have massive object stages. Usually the light house is attached to the back of the microscope. The light is directed through the light field aperture into an area in which color and reduction filters can be used. The light then passes the aperture diaphragm of the condenser and then hits a semi-transparent mirror that deflects most of the light towards the objective. From there it is focused on the object through the lens . The light is reflected by this and passes through the lens again. The light passes through the semi-transparent mirror again and is deflected towards the eyepieces . After passing through the eyepieces, the light hits the viewer's retina . With many (better) reflected light microscopes, the light house can also be implemented in such a way that it allows transmitted light. Of course, this then requires a suitable specimen table.
In the case of inverted incident light microscopes, the object table usually represents the highest point of the device. The object lies with the surface to be microscoped facing down on the object plate and is also irradiated from below. Otherwise, the illumination and imaging beam paths are basically the same, just rotated by 180 °.
When handling the two device types, the following differences primarily arise in practice:
- With inverted incident light microscopes, the size of the objects is only limited by the carrying capacity of the object table. In this way, larger objects can be examined without having to shred them (and thus possibly destroy them).
- With inverted reflected light microscopes, the objects are always flat and at right angles to the objective. There is no need to squeeze it onto plasticine or the like, as is usually necessary with upright reflected light microscopes.
- The objectives are clearly exposed in inverted incident light microscopes, which means that falling objects or liquids dripping from the object can damage the front lens. The lenses of inverted reflected light microscopes also collect dust much more easily.
Types of lighting
Typical illumination modes in reflected light microscopy are:
- Dark field
- Polarization contrast
- Differential interference contrast (DIK / DIC)
- Phase contrast
scope of application
Incident light microscopy is particularly useful for opaque objects, for example in metallography ; It also has advantages in fluorescence microscopy and is used for this. In medicine, the procedure is used in dermatoscopy , in which dermatologists examine changes in the skin of their patients using a hand-held incident light microscope. It is also used in ophthalmology in the form of a so-called slit lamp . In mineralogy , incident light microscopy and the polarization microscope are used to identify ore minerals (vertical illuminator ), with properties such as bireflection , internal reflections and degree of reflection being determined. In geology , it is an important method in coal petrography .
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- Jörg Haus: Optical microscopy, functionality and contrasting methods . John Wiley & Sons, 2014, ISBN 978-3-527-41286-0 ( limited preview in Google Book Search).
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