Is image distance always taken as negative for concave mirror or lens?

Answer 1

In the case of concave mirrors, the image distance is typically taken as negative when the image is formed on the same side as the object (real image). However, for virtual images formed by concave mirrors, the image distance is considered positive. For concave lenses, the image distance is always taken as negative because they always produce virtual images on the same side as the object. Therefore, while there are specific conventions, the sign of the image distance depends on the type of image and optical device being used.