What should not be controlled by the aperture diaphragm?

The aperture diaphragm is a crucial component in optical systems, particularly in microscopy. Its primary function is to regulate the amount of light that enters the optical path, impacting several aspects of image quality.

Controlling brightness is indeed one of the roles of the aperture diaphragm, as it adjusts the light intensity reaching the specimen or the imaging sensor. However, the resolution of the image, contrast, and the field of view are influenced by other factors such as lens quality, optical setup, and the specifics of the imaging system.

Resolution refers to the ability to distinguish between two closely spaced points, which is determined by the numerical aperture of the objective lens and the wavelength of light used, rather than solely by controlling light intensity. Contrast, the difference between the light and dark parts of an image, is affected by how the light interacts with the specimen and the imaging system's sensitivity to those variations. The field of view pertains to the observable area seen through the optics, which is defined by the optical design rather than light intensity.

Thus, the brightness is the aspect that directly correlates with the aperture diaphragm’s function, making it appropriate to say it should not be controlled by the aperture diaphragm in the context of the other options provided.