What signs for object distance and image distance must we take for a myopic eye and a hypermetropic eye?
According to the cartesian rules, when the image is formed on the left side of the lens the distance is taken negative. To correct the myopic problem, concave lens are needed and concave lens forms the image on the same side where the object is placed. Object is always placed on the left side of the lens. Hence the image distance is taken negative in the myopic problem.
A person with hypermetropia can see distant objects clearly, but cannot see nearby objects distinctly.
The defective near point is taken as the image distance is hypermetropia. As the defective near point is at the left side of the lens, it is taken as negative.
Object distances are always taken as negative .