Which part of a microscope is primarily responsible for adjusting the brightness of the image?

• A. Diaphragm (Iris diaphragm)
• B. Coarse focus knob
• C. Objective lens
• D. Eyepiece (Ocular lens)

Answer: (A)

Verified step by step guidance

1. Understand the function of each microscope part listed in the problem: The diaphragm (iris diaphragm) controls the amount of light passing through the specimen, the coarse focus knob adjusts the focus, the objective lens magnifies the image, and the eyepiece (ocular lens) is used to view the magnified image.
2. Identify which part directly influences the brightness of the image. Brightness is determined by the amount of light reaching the specimen, which is controlled by the diaphragm.
3. Recall that the diaphragm (iris diaphragm) can be adjusted to increase or decrease the light intensity by opening or closing its aperture.
4. Eliminate the other options: The coarse focus knob does not affect brightness but adjusts focus, the objective lens magnifies the image without altering brightness, and the eyepiece is used for viewing but does not control light intensity.
5. Conclude that the diaphragm (iris diaphragm) is the correct answer because it is specifically designed to regulate the brightness of the image by controlling the light passing through the specimen.