Concave lens is used to correct near sightedness or myopia.

A short sighted person uses a spectacle of power $-0.4 \mathrm{D}$ to see very distant objects. How far can he see without using spectacle?

An object is placed at a distance $24 \mathrm{cm}$ in front of a convex lens of focal length $8 \mathrm{cm}$.
(i) Calculate the distance of the image from the lens.
(ii) Calculate the magnification of the image.

A virtual, diminished image is formed when an object is placed between the optical centre and the principal focus of a lens.
(i) Name the type of lens which forms the above image.
(ii) Draw a ray diagram to show the formation of the image with the above stated characteristics.  

A converging lens forms a three times magnified image of an object, which can be taken on a screen. If the focal length of the lens is $30 \mathrm{cm}$, then the distance of the object from the lens is _____.