Many optical instruments consist of a number of lenses. They are combined to increase the magnification and s…

Many optical instruments consist of a number of lenses. They are combined to increase the magnification and sharpness of the image. The net power $(P)$ of the lenses placed in contact is given by the algebraic sum of the powers of the individual lenses $P_1$, $P_2$, $P_3$ ... as $$P=P_1+P_2+P_3\dots$$ This is also termed as the simple additive property of the power of lens, widely used to design lens systems of cameras, microscopes and telescopes. These lens systems can have a combination of convex lenses and also concave lenses.