Infinity corrected objectives are used in a wide variety of imaging and laser focusing applications. Light rays leaving the objective’s rear aperture are collimated, so that for imaging applications, a secondary lens (usually called a tube lens) is needed in order to focus the collected light from the specimen onto the sensor. The labeled magnification is calculated, assuming the objective is being used with a tube lens of a particular focal length by design. When a tube lens of a different focal length is used, the magnification will need to be adjusted accordingly. As an advantage over finite conjugate objective lenses, a variety of auxiliary optical components, such as optical filters and polarizers can be inserted between the infinity objective lens and the tube lens without altering how the beam propagates and forms the image down the optical path. In laser applications such as optical tweezers and laser cutting, laser beams entering the rear aperture of an infinity objective can be tightly focused to a diffraction-limited spot, providing concentrated optical power and excellent resolution.

The LI series of microscope objectives can be used with the 900 series spatial filter system. By selecting an objective and corresponding pinhole, the laser beam can be spatial filtered such that the output beam quality is better. For a tutorial on spatial filters see Spatial Filter Technical Note.