Final answer:
Contrast in light microscopy is most commonly obtained using phase contrast and differential interference contrast, both of which enhance image clarity of structures based on refractive index differences. Fluorescence and dark field microscopy offer alternative contrast methods by employing either fluorescent stains or scattering light against a dark background.
Step-by-step explanation:
Two ways to obtain contrast in light microscopy are through phase contrast and differential interference contrast (DIC). Phase contrast utilizes differences in the refractive indices of specimens to enhance the visibility of transparent and unstained samples. It achieves this by shifting the phase of light that passes through structures within the specimen. In contrast, DIC exploits the same principle but uses polarized light and additional optical components to produce a three-dimensional-like image with color and enhanced edge contrast for structures within the cell.
Fluorescence microscopy uses fluorescent stains that emit light when illuminated with specific wavelengths, providing high-contrast images against a dark background. Dark field microscopy also increases contrast by using a dark background, but it works by scattering light off the specimen such that only light that is scattered by the specimen enters the objective, making the specimen appear bright on the dark background. These methods allow researchers to examine cellular details that would otherwise be difficult to see using traditional brightfield microscopy alone.