Special optical techniques of image formation
When a light ray passes through a transparent object having a different refractive index from that of the medium, it undergoes phase changes (as discussed in Section 2.1) which, unlike the case of amplitude changes, are not revealed in the visible image. Consequently, a transparent object such as a tissue section will give an image which is poor in contrast and yields little information. By reducing the aperture of the illumination beam by means of the aperture diaphragm, contrasts may be enhanced (Figure 2.2A) but in the end the result will remain unsatisfactory. The formation which follows from the modulation of the illumination beam by the object remains concealed in the image.
KeywordsDifferential Interference Contrast Phase Plate Optical Path Difference Entrance Pupil Wollaston Prism
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