Related applications of Huygens eyepiece

Huygens eyepiece can be used for both observation and photography. When the image formed by the objective lens is in the focus of the objective lens, it becomes an enlarged virtual image, which can be observed by a microscope. When the image formed by the objective lens is not in the focus of the objective lens, it becomes an enlarged real image, which can be used for photomicrography. Huygens eyepiece cannot be used as a magnifying glass alone because its focus is between the two lenses. This kind of eyepiece which cannot be used as a magnifying glass alone is called a negative eyepiece. Huygens eyepiece has no aberration correction, and is only suitable for medium and low magnification achromatic objective lens. Its magnification is generally not more than 15 times.