The image of the objective of the eyepiece is called exit aperture. All the rays coming from the object pass through the exit aperture after refraction from the objective. Therefore, this is an ideal condition for seeing with our eyes. If we keep our eyes too close to the eyepiece, the eyepiece will not be able to receive much light and the area of vision will also reduce. If we place our eyes on the exit aperture and the area of the pupil of our eye is greater than or equal to the area of the exit aperture, then our eyes will capture all the rays refracted from the objective. The exact location of the aperture generally depends on the distance between the objective and the eyepiece. When we look through a microscope by placing our eye on one end of it, the ideal distance between the eye and the eyepiece is inherent in the design of the instrument.
