Our line of adjustable eyepieces fits any international standard microscope with a 23mm inner diameter eyepiece tube. They are specifically designed to accept glass disc reticles with 21mm or 19mm diameters. The diopter adjustable eye lens allows the reticle to be brought into sharp focus when superimposed on the real image plane, which is often difficult to achieve with fixed focus eyepieces. The reticle is held in place with a threaded retainer ring. For Kellner and Wide Field (WF) designs, it is easily installed from the bottom of the housing. For Periplan designs, the bottom part of the housing must be removed to install the reticle between the eye lens and field lens. Our Wide Field design incorporates the eye lens and field lens in the adjustment portion (top) of the eyepiece. This is a more complex design that allows for superior focus adjustment and image quality. All are DIN format.