Microscope as a Light Bench

The Light Microscope is basically a optical bench designed for the investigation of the characteristics of particles. The first filter pack can control the wavelengths used, type of polarization (linear to circular), control of tube scatter, and framing. The second filter pack is at the plane of the substage iris. This is a location where the "diffracted" beam is in focus. It is the location for the phase anulus when using phase contrast. It is the location for Rhineberg filters, interference system filters, and other filters that change the image by manipulating parts of the diffraction pattern generated by the particle and collected by the objective. This location can also be used to generate different types of dispersion staining. The angle at which the beam of light strikes the particle can be changed from parallel to the optical axis of the microscope to angles greater than the numerical aperture of the objective (about 65 degrees for a dry mount objective). Transmitted brightfield, transmitted oblique, darkfield oblique, to full darkfield, and other combinations of illumination can be controlled at this location. The particle on the stage can be illuminated from the side by an accessory illuminator from grazing incidence to oblique reflected darkfield. A ringlight can be attached to the objective to generate full reflected darkfield illumination. The angle of the reflected beam can be controlled to some extent by moving the ringlight up or down the collar of the objective. The back focal plain of the objective is another diffraction focal plane. A number of filters can be place at this location, including the phase plate for phase contrast microscopy and filters for various types of interference systems. This is another location where optical stops can be used to generate dispersion staining. Additional filters can be placed in the light path above the objective, like compensator plates and polarizing filters for optical crystallography. The Bertrand Lens can be inserted to bring the diffraction focal planes into focus for the observer. Graticules are placed at the focal plane of the eyepiece to facilitate various measurement methods applied to the field of view. The image is then transferred to the human visual system to be refined by a complex system of built-in algorithms, both bottom-up and top-down, to create the final perceived image. What is finally seen is dependent on the skill and knowledge of the microscopist, just as an infrared spectrum of an organic compound must be interpreted by one knowledgeable in reading such data. The human visual system is not a camera.