Contrast of optical microscope

Contrast in Optical Microscope

The contrast in Optical microscope, because of the specific technique is called Phase Contrast of Optical Microscope.

This indispensable technique of nowadays was first utilized by the awarded one in 1953 by the Nobel Prize, Frits Zernike.

This optical microscopy technique consists in reinforcing the contrast between the transparent specimens with the images of living cells, microorganisms, and other samples.

It has the important useful advantage that living cells and tissues do not need to be killed, fixed or prepared in laboratory so that can be analyzed in their natural state, facilitating the procedure. This will also be better because no chemicals or other not biologic products will be used, so the sample will remain the most natural possible, and this will lead us to the better understanding of the experience.

The technique is based on the variations in phase of the amplitude change and the most important concept of the phase contrast microscope design is the isolation of wavefronts, both surround (undiffracted) and diffracted, that arise from the sample. To differentiate intensity profiles between a sample and its surroundings, the undeviated light must be reduced and the phase retarded by a quarter-wave retardance. A brightfield illumination microscope can be upgraded to a brightfield-phase microscope with the introduction of two components to the optical train.

A typical phase contrast image has a neutral background and surrounding with varying contrast where light is altered by the sample.

Two very common effects seen in a phase contrast image are halo and shade-off patterns. These occur when the infinite-conjugate focal point does not match for the specimen and background. Although these are common and expected in phase contrast images, they have the disadvantage of diminishing the appearances of details. A bright phase contrast halo is typically visible at a boundary between strong and weak specimen features. These halos are evident due to the circular phase-retarding rings. Specialized objectives, known as “apodizing phase contrast objectives”, are manufactured to reduce this phenomenon (reducing this way the disadvantage). Superscript text This technique was first used in 1930, and in the last 80 years has been developed, according to the necessities of the scientific society, and nowadays is used by millions of people.