Bright-field microscopy

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. light microscope 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 therefore consists of: a transillumination light source, commonly a halogen lamp in the microscope stand; a condenser lens, which focuses light from the light source onto the sample; an objective lens, which collects light from the sample and magnifies the image; oculars and/or a camera to view the sample image. Bright-field microscopy may use critical or Köhler illumination to illuminate the sample. 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. Image:Paper_Micrograph_Bright.png|Bright-field illumination, sample contrast comes from [[absorbance]] of light in the sample Image:Paper_Micrograph_Cross-Polarised.png|[[Polarized light microscopy|Cross-polarized light]] illumination, sample contrast comes from the rotation of [[Polarization (waves)|polarized]] light through the sample Image:Paper_Micrograph_Dark.png|[[Dark-field microscopy|Dark-field]] illumination, sample contrast comes from light [[Scattered radiation|scattered]] by the sample Image:Paper_Micrograph_Phase.