This part of ISO 9345 specifies the imaging distances of objectives, eyepieces and the focal length of "normal" tube lenses of microscopes with infinity-corrected optical systems. NOTE A specific combination of eyepiece, objective, and tube lens is frequently used to correct aberrations. Therefore the combination of an objective from one manufacturer and the tube lens or eyepiece from another manufacturer, although conforming to this part of ISO 9345, can cause errors in magnification and/or in optical performance.