Why would I use a multi-element magnifier?

Multi-element magnifiers are required for larger magnification systems. They are also designed for better resolution and for correcting chromatic and spherical aberrations, as well as distortion. As a result, they have much better image quality and flatter fields. As more power and quality are needed, the required design starts to change from a magnifier to a microscope. Compound magnifiers are actually the basis for "simple microscopes."