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condenser
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Diagram showing how a microscope forms images according to Abbe Theory, with labeled components including condenser, specimen, objective lens, and focal plane, plus insets illustrating constructive and destructive interference and spatial frequency patterns.
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condenser

optics
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Diagram showing how a microscope forms images according to Abbe Theory, with labeled components including condenser, specimen, objective lens, and focal plane, plus insets illustrating constructive and destructive interference and spatial frequency patterns.
image formation in a microscope; Abbe theory Image formation in a microscope, according to the Abbe theory. Specimens are illuminated by light from a condenser. This light is diffracted by the details in the object plane: the smaller the detailed structure of the object, the wider the angle of diffraction. The structure of the object can be represented as a sum of sinusoidal components. The rapidity of variation in space of the components is defined by the period of each component, or the distance between adjacent peaks in the sinusoidal function. The spatial frequency is the reciprocal of the period. The finer the details, the higher the required spatial frequency of the components that represent the object detail. Each spatial frequency component in the object produces diffraction at a specific angle dependent upon the wavelength of light. Here, for example, a specimen with structure that has a spatial frequency of 1,000 lines per millimetre produces diffraction with an angle of 33.6°. The microscope objective collects these diffracted waves and directs them to the focal plane, where interference between the diffracted waves produces an image of the object.

In optics, a condenser is a lens or a system of lenses used to focus light onto a specimen or film. In microscopes, the condenser is located beneath the stage and concentrates light to provide bright, uniform illumination of the object being viewed. This can be achieved through methods like critical illumination, where the light source's image is focused directly onto the specimen, or Köhler illumination, which focuses the light onto the objective lens's entrance pupil for more uniform lighting.12

Condensers can also be found in photographic enlargers, where they focus light through the film and towards the enlarging lens. This is particularly useful for producing prints with fine detail and high contrast. Early condensers were often single lenses, but more complex designs have been developed over time for specific applications, including dark-ground condensers for observing specimens against a black background.21

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4 Britannica Sources
  1. condensing lens
  2. microscope - The illumination system
  3. enlarger
  4. optics - Nonclassical imaging systems

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