A specially designed lens that mounts under the stage and is usually movable in the vertical direction. The abbe condenser has an iris type aperture to control the diameter of the light that enters the lens system. By changing the size of the iris and moving the lens toward or away from the stage, the diameter and focal point of the cone of light that goes through the specimen can be controlled. Abbe condensers become more useful at magnifications above 400x. The condenser lens system should have a numerical aperture equal to or greater than the N.A. of the objective lens being used. All of our microscopes that have 1000x magnification use Abbe condensers with a 1.25 N.A. There are two types of condensers - one is a spiral type that you turn to move it up or down and the other is on a rack and pinion system and is controlled with a condenser focusing knob.
An Abbe condenser is a component of a microscope. It is mounted below the stage of the microscope, and concentrates and controls the light that passes through the specimen and enters the objective. It has two controls, one which moves the Abbe condenser closer to or further from the stage, and another, the iris type diaphragm, which controls the diameter of the beam of light.