Key Words: Illumination, fly-eye lens
Definition:A technique for uniformly illuminating the specimen from non-uniform light source (e.g. a coiled filament lamp)
TECHNOLOGY:
Köhler illumination was first described by August Köhler in 1893, and is still the accepted (almost exclusively) method of modern microscope illumination. Köhler illumination eliminates uneven illumination in the field of view so that all parts of the light source contribute to specimen illumination. There are two types of Koehler illumination, one method in which light is transmitted through the specimen (transmitted) and one method where it is reflected from the specimen (incident). Transmitted Koehler illumination is used for transparent or semi-transparent specimens, while incident Koehler illumination is useful for objects such as metal, which do not transmit light.
Köhler illumination requires a collector lens in or near the lamphouse that can be adjusted to focus an image of the lamp filament at the front focal plane of the condenser where the aperture diaphragm is positioned. If the lamp filament image is centered properly and fills the aperture completely, illumination of the specimen plane is bright and even. To ensure that the filament image appears in the condenser focal plane, the height of the condenser must often be adjusted. This critical adjustment brings two sets of conjugate focal planes (referred to as the field set and the aperture set) into precise physical locations within the microscope optical train, and maximizes microscope performance.
APPLICATIONS:
Köhler illumination is used in both reflected-light and transmitted light microscopy
MICROSCOPE CONFIGURATION:
Optical components in the microscope system must be aligned correctly for optimal microscope imaging.
RECOMMENDED SYSTEM:
Please consult your local Nikon representative for advice suited to your imaging needs.
LINKS:
Microscope alignment for Köhler illumination [microscopyu]