A slide projector employs a single thin converging lens of focal length 80mm to produce images on a far-away screen.
(All distances are measured from the lens along its principal axis.)
(1) Calculate the distance between the slide and the lens that will allow the projected image to form essentially at infinity so that the screen can be placed arbitrarily far away without the need for refocusing.
(2) A presenter unintentionally positions the slide 85mm from the lens instead. Determine the new image distance.
(3) State whether the image formed in part (b) is real or virtual and describe its orientation relative to the original slide. Justify your answer based on the sign of the calculated image distance.