Bright-field microscopy is the simplest of all the optical microscopyillumination techniques. Sample illumination is transmitted 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 lightmicroscopes, 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 path
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:
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 livecells in many situations. Bright-field illumination is useful for samples that have an intrinsic color, for example chloroplasts in plant cells. tissue paper " align="center"> Image:Paper_Micrograph_Bright.png|Bright-field illumination, sample contrast comes from absorbance of light in the sample Image:Paper_Micrograph_Cross-Polarised.png|Cross-polarized light illumination, sample contrast comes from the rotation of polarized light through the sample Image:Paper_Micrograph_Dark.png|Dark-field illumination, sample contrast comes from light scattered by the sample Image:Paper_Micrograph_Phase.png|Phase-contrast illumination, sample contrast comes from interference of different path lengths of light through the sample
Simplicity of setup with only basic equipment required.
Living cells can be seen with bright-field microscopes.
Limitations
Very low contrast of most biological samples.
The practical limit to magnification with a light microscope is around 1300X. Although higher magnifications are possible, it becomes increasingly difficult to maintain image clarity as the magnification increases.
Samples that are naturally colorless and transparent cannot be seen well, e.g. many types of mammalian cells. These samples often have to be stained before viewing. Samples that do have their own color can be seen without preparation, e.g. the observation of cytoplasmic streaming in Chara cells.
Use of sample-staining methods for use in microbiology, such as simple stains and differential stains.
Use of a colored or polarizing filter on the light source to highlight features not visible under white light. The use of filters is especially useful with mineral samples.
