A student sets the cross-hairs of an eyepiece in line with an image that he is measuring. He then notes that when he moves his head slightly to the right, the image moves slightly to the left (with respect to the cross-hairs). Therefore the image is:

Question

Quizplus · Accepted Answer

If the image moves in the opposite direction to the observer's head movement, then the image is closer to the observer than the cross-hairs. This is because, as the observer moves their head, their eyes shift position relative to the eyepiece, causing the angle of incidence of light on the eye to change. If the image were farther away, the angle of incidence would be more parallel and the image would not appear to move as the observer's head moved.

A Student Sets the Cross-Hairs of an Eyepiece in Line