American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

Which component of a brightfield microscope is used to manipulate contrast?

1. Stage clips

2. Condenser aperture diaphragm

3. Objective lenses

4. Focusing knobs

The correct answer is: Condenser aperture diaphragm

The component of a brightfield microscope used to manipulate contrast is the condenser aperture diaphragm. This diaphragm helps control the amount of light that passes through the specimen by varying the diameter of the light beam coming from the condenser. By adjusting this diaphragm, the microscopist can optimize the contrast of the image being viewed. When the diaphragm is closed slightly, it increases contrast by reducing the amount of light and enhancing the differences in optical density between the specimen and the background. This is particularly useful when examining transparent specimens that may otherwise appear faint. Other components mentioned have different functions: stage clips secure the slides in place, objective lenses magnify the specimen, and focusing knobs adjust the focal length to bring the specimen into sharp focus. These components do not actively manipulate the light intensity in a way that enhances contrast in the images produced by the microscope.