Mørkfeltbilder

Mørkfeltbilder, a term originating from Norwegian, translates to "dark field images" and refers to a technique used in microscopy and imaging to enhance the contrast of transparent specimens. In this method, the illumination source is positioned such that only light scattered by the specimen enters the objective lens. Unscattered light, which would normally illuminate the background brightly, is blocked. This creates a dark background against which the specimen's structures appear luminous and well-defined.

The principle behind mørkfeltbilder is similar to how dust motes become visible in a beam of sunlight; the particles scatter light, making them stand out against the dark surroundings. This technique is particularly useful for observing unstained, transparent, or weakly absorbing samples that might be difficult to see with conventional brightfield microscopy. Examples of applications include viewing live microorganisms, cellular components, or fine details on surfaces without the need for staining, which can sometimes alter or damage the specimen.

Mørkfeltbilder can be achieved using specialized condenser rings or apertures in a microscope. These components are designed to block direct illumination from reaching the objective lens. Light is then directed at an oblique angle towards the specimen. Any light that is diffracted or scattered by the specimen's edges, refractive index variations, or internal structures is then collected by the objective. The resulting image typically shows bright, shimmering details against a black background, offering a distinct visual representation of the sample's morphology and composition.