Final answer:
The ability of an image intensifier to increase the image's overall illumination level is referred to as brightness gain. It is achieved through the combination of flux gain and minification gain. In microscopy, various adjustments to the lighting system, including condenser lenses and iris diaphragms, are used to maintain optimal illumination for magnified images.
Step-by-step explanation:
The ability of an image intensifier to increase the overall illumination level of the image is known as brightness gain. Brightness gain refers to the factor by which the brightness of the image is increased compared to the brightness of the input scene. It combines the effects of flux gain, which is a measure of how much the image intensifier amplifies the number of photons, and minification gain, which is the concentration of these photons into a smaller area, resulting in increased brightness per unit area.
In microscopy, intense lighting is often required for highly magnified images, as magnification can cause the images to become dimmer due to less light per unit area. To address this, condenser lenses are used to concentrate light on the specimen, and different types of condensers are suitable for various applications depending on whether the specimen is examined by transmission, scattering, or reflecting. Methods to adjust the illumination include changing light intensity with a dimmer switch or rheostat, or manipulating the condenser lens position and the iris diaphragm.