Let’s see what the value and sign of the magnification of a lens tell us about the type of lens and image formed.
1) If the magnification ‘m’ has a positive value, the image is virtual and erect. And if the magnification ‘m’ has a negative value, the image will real and inverted.
2) A convex lens can form virtual images as well as real images, therefore, the magnification produced by a convex lens can be either positive or negative.
3) A convex can form images which are smaller than the object, equal to the object, or bigger than the object, therefore magnification ‘m’ produced by a convex lens can be less than 1, equal to 1, or more than 1.
4) A concave lens, however, forms only virtual images, so the magnification produced by a concave lens is always positive.
5) A concave lens forms images that are always smaller than the object, so the magnification ‘m’ produced by a concave lens is always less than 1.
Related Posts you can refer to understand the rules of magnification by spherical lenses.