A few words for the beginners
The most important feature of a microscope is of course to give a larger image, and the increased image is probably the determining factor of this device. A very important parameter of optics is "aperture". We will not bore you with the formulas, in simple words - the more the aperture is, the stronger the lens refract light rays and the more of those rays pass through the lens.
A simple glass lens (the "dry", as experts say) can reach the aperture value of 0.95. If you get close to 0.65, the lens can be classified as a high aperture lens. But really high values of aperture can be achieved by immersion lenses, which, unlike the "dry" ones, contain a so-called immersion liquid. The liquid improves the optical parameters (the aperture can reach the values of 1.40)
In addition, in order to achieve quality, and above all see clear images, it is very important to have a high resolution microscope. It is required not only eliminating the distortions associated with inaccuracies in the lenses, but somehow compensating the dispersion of light, ie expansion of the "white" spectrum of seven colors of the rainbow, arises due to unequal refraction in the glass of different light waves. Achromatic lenses are used for this purpose, they only slightly distort the color. The "image" in the microscope with achromatic lens accurately conveys the colors of the viewed object.
And finally, last but not least, an absolutely necessary part of a microscope is a source of light. The simplest source would be a mirror, which directs light to the object being studied, the more advanced types of microscopes use a special bulb with predetermined parameters of the spectrum and brightness.