Can lenses be used as a visual aid ?
Lenses can be used to magnify smaller things, and to see distant objects clearly. Their uses as optical instrument are illustrated below: –
Simple magnifier:
A simple magnifier consists of a converging lens. The lens is held such that object is adjusted between lens and its focus so that a virtual, magnified image is formed. For distinct vision, the image is adjusted to be at a distance of about. 25 cm (least distance of distinct vision for human eye = 25cm)
Hence magnification is nearly $ \displaystyle m = (1 + \frac{25}{f}) $