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Brightfield

The bright field microscopy (Brightfield) is the simplest of microscopy techniques. This technique is useful for all those samples that have a high enough contrast to be distinguished from the background of the preparation, or for specimens that can be easily colored with dyes. The contrast of the subject is caused by the absorption of some of the light transmitted in areas of high density of the sample, the result is a dark image on a light background, hence the name. In this technique, you can increase the contrast closing the aperture of the condenser, this, however, results in a reduction of the resolution and introduces artifacts and diffraction, natural colors become less visible and the whole image loses brightness. The closing ratio, generally, a iris capacitor In brightfield microscopy, the closure of the condenser iris diaphram should not exceed third of total, preferably ¼.
To overcome the limits of brightfield microscopy, different optical techniques of contrast were invented (Phase Contrast, Darkfield, DIC ...).