The field of view of the microscope is a good example of a virtual image. When the eye operates in conjunction with a lens to form an image on the retina, the visual sensation is as if the image existed in space. That its apparent location is very definite is proved when a pin can be made to coincide with the mirror (virtual) image of another pin that is seen by looking at a sheet of glass acting as a mirror.
With a lens system a virtual image can be definitely located as by graphically tracing rays back to a focus. In a microscope, if the eye is relaxed as it should be, the virtual image will be at infinity. Measurements show that most observers place the aerial image at 20-25 feet, some as close as seven, because of partial accommodation.