Final answer:
The component used to control light in a microscope from the condenser is called the diaphragm or iris diaphragm, which is essential for proper image contrast and brightness at various magnifications.
Step-by-step explanation:
The shutter attachment used to control the amount of light that comes from the condenser in a microscope is called the diaphragm, also known as the iris diaphragm. This component can be adjusted to either allow more light, which is useful for higher magnifications with small apertures, or to decrease the light when using lower magnifications. The position of the diaphragm affects image contrast and brightness, which underscores its role in achieving the best possible image quality.