A few tests ensure the optics produce useful images of the parts or components you need to inspect. A typical microscope target used to help you evaluate optics provides light and dark patterns and characters. Patterns of line pairs, circles, dots, and radial lines are also available. Because the optical system creates an image of a real object, you can't evaluate optical quality without using a target object. Targets can be either highly stylized or realistic.
Stylized targets make it easy to see particular effects.
Patterns of equally spaced black and white lines help you find the microscope's limit of resolution. Finely ruled rectangular grids bring out distortion effects. Although stylized targets help ferret out optical flaws or determine the degree of imaging errors, they don't give you a good idea of what real samples will look like. For that type of test, you need products, components, or assemblies of the type you want to inspect. Images should look real.