The smaller the focus of a convex lens, more its magnifying capacity, so why don't we use magnifying glasses with very small focal length?

Q.

The smaller the focus of a convex lens more will be its magnifying capacity, so why don't we use magnifying glasses with very small focal length?

Q. (a) Explain what is meant by a virtual, magnified image.
(b) Draw a ray diagram to show the formation of a virtual magnified image of an object by a convex lens. In your diagram, the position of object and image with respect to the principal focus should be shown clearly.
(c) Three convex lenses are available having focal lengths of 4 cm, 40 cm and 4 m respectively. Which one would you choose as a magnifying glass and why?

Q. A card sheet divided into squares each of size $1m{m}^2$ is being viewed at a distance of $9cm$ through a magnifying glass (a converging lens of focal length $9cm$) held close to the eye and the magnifying glass if the virtual image of each square is to have an area of $6.25m{m}^2$. Would you be able to see the squares distinctly with your eyes very close to the magnifier?

Q. A double convex lens of focal length 15 cm is to be used as a magnifying glass. In order to produce an erect image which is 3 times magnified, the distance between the object and the lens should be