Although most monocular microscopes have a single lens they can also have compound lenses. When they have one lens they are also referred to as a simple microscope. There are various types of monocular microscopes such as jeweler’s loupes, magnifying glasses, or reading glasses. Many people do not consider these as a microscope but they are because they let you see smaller things through one lens to make things appear larger.
A monocular microscope with a single lens can cause various types of image distortions so they have limited uses. Two examples of these image distortions include spherical aberration, which distorts the focus and chromatic aberrations, which distorts the color. When a monocular microscope has compound lenses it does not make it a compound microscope unless it has only one eyepiece. It is normally considered a compound lens magnifier. This is a single array of simple lenses with a common access. Using a compound lens can correct some of the single lens aberrations, or distortions, along with giving magnification at a higher power. They can also be handheld giving it the same flexibility as a jeweler’s loupe or magnifying glass.
When the monocular microscope is considered a compound microscope it has a minimum of two-lens array with one lens being the ocular lens, which is the one that you look through. The other lens would be the objective lens, which is positioned near the specimen or object you are looking at.
When buying your first monocular microscope make sure that you get one that is best suited for your needs, is affordable, and has optics of high quality. You also want to make sure that it has a reliable warranty. Purchase one made by a company that manufactures optics that is professional grade. Buying from chain stores, they usually have poor optics and made from cheap parts.