Bright-field microscopy (BF) is the simplest of all the optical microscopy illumination techniques. Sample illumination is transmitted (i.e., illuminated from below and observed from above) white light, and contrast in the sample is caused by attenuation of the transmitted light in dense areas of the sample. Bright-field microscopy is the simplest of a range of techniques used for illumination of samples in light microscopes, and its simplicity makes it a popular technique. The typical appearance of a bright-field microscopy image is a dark sample on a bright background, hence the name.
The first simple microscope was invented by two Dutchmen, Zaccharias Janssen and his father, Hans, by testing lenses in a tube and observed that the objects nearby were now larger. This was not included as a scientific discovery but it paved the start of a path. Further down the path a man named Antony Van Lewnehoueek created the first simple microscope that allowed him to observe pond water. This microscope was made with a double cortex lens and silver plates.
A bright-field microscope has many important parts including; the condenser, the objective lens, the ocular lens, the diaphragm, and the aperture. Some other pieces of the microscope that are commonly known are the arm, the head, the illuminator, the base, the stage, the adjusters, and the brightness adjuster. The condenser of the microscope allows no extra light from the surroundings to interfere with the light path and condenses the light from the illuminator to make a uniform light path. The objective lens and the ocular lens work together, the ocular lens is ten times magnification and the ocular lens has different numbers by how much they can go up to, the highest being 400, the two together make up to 4,000x magnification. The aperture is a part of the diaphragm that controls the diameter of the beam passing through the sample at a time. The adjusters move the stage up and down towards the objective lens and the arm, head, and base.[1]
The light path of a bright-field microscope is extremely simple, no additional components are required beyond the normal light-microscope setup. The light path consists of begins at the illuminator or the light source on the base of the microscope, often time a halogen lamp is used. Then the light travels through the objective lens into the ocular lens to view the sample. Bright-field microscopy may use critical or Köhler illumination to illuminate the sample.[2]
Bright-field microscopy typically has low contrast with most biological samples, as few absorb light to a great extent. Staining is often required to increase contrast, which prevents use on live cells in many situations. Bright-field illumination is useful for samples that have an intrinsic color, for example mitochondria found in cells.
Bright-field microscopy is a standard light-microscopy technique, and therefore magnification is limited by the resolving power possible with the wavelength of visible light.
Bright-field microscopes are very simple to use and can be used to view both stained and unstained specimens. The optics do not change the color of the specimen, making it easy to interpret what is observed.