A microscope objective lens is a crucial part of a microscope's optical system, forming the initial magnified image of a specimen. It consists of a complex assembly of lenses, positioned close to the sample, that gathers light from the object to create a high-resolution image. Key specifications include its magnification, which determines how much the image is enlarged, and its numerical aperture (NA), a measure of its light-gathering ability that dictates the microscope's resolution. The objective also contributes to optical performance by correcting for various aberrations and can be classified by its design, such as standard or plan lenses, which provide a flatter field of view.