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

What should not be controlled using the aperture diaphragm?

1. Focus on the specimen

2. Control brightness of light

3. Adjust magnification

4. Enhance contrast

The correct answer is: Control brightness of light

The aperture diaphragm is primarily used in microscopy to control the amount of light that reaches the specimen, which can directly influence the brightness and contrast of the image. However, its primary function is not to adjust the brightness of the light source itself but rather to regulate the diameter of the beam of light that transmits through the condenser. Managing brightness is typically achieved through other means, such as adjusting the intensity of the light source or using neutral density filters. Therefore, while the aperture diaphragm can affect how bright or dim an image appears by limiting or allowing more light through, it does not serve as the primary control for brightness itself. In contrast, focusing on the specimen directly influences clarity and resolution, and adjusting magnification increases or decreases the size of the observed features. Enhancing contrast improves the visualization of structures and can be optimized by adjusting the light passing through the specimen, which is influenced by the aperture diaphragm settings. Thus, controlling brightness via the aperture diaphragm is not its designed intent, highlighting why this response is the most fitting.