What is an infinity-corrected objective?

An infinity-corrected objective is a microscope objective designed to be used in conjunction with an infinity-corrected tube that will give you a longer working distance than a normal DIN-type objective. In most microscopes, the tube length is empty and all the magnification is done using the lenses in the eyepiece and the objective. The image from an infinity-corrected objective is collimated (parallel light) prior to being imaged by the secondary lens assembly. With an infinity-corrected system (objective and tube), a lens system is actually contained within the tube, which is required in order to form an image from the objective. This allows the objective and the entire microscope to be placed farther away from the sample, allowing users the added room to maneuver the sample being viewed. The major disadvantage of using infinity-corrected objectives is that you must have a tube lens or the system will not focus.