PE Lens attachments go onto the base of the system body tube and are available in a variety of magnifications. The normal working distances of the zoom system is approximately 90 mm. Lens attachments thread onto the bottom of the zoom system and can extend the working distance out to 350 mm or pull it in as close as 35 mm. The extending lenses (.75X, .5X, and .25X) decrease the overall magnification, and increase the field of view. The shortening lenses (1.5X, and 2.0X) increase the magnification and decrease the field of view. As the working distance goes from long to short, the "taking N.A." of the system increases, resulting in an increase in resolving power.