Magnifying Loupes - Features: Set and Forget™ optics, Dual hinge design, Locking interpupillary knob, Double locking convergence angle. Benefits: Optics are quickly and easily locked into place, Allows for easy flip up of optics, Allows for secure adjustments of your settings, Provides stable alignment of optics. Choosing the right loupe: follow these two steps for a perfect match: Step 1: Choose magnification. Start with the lowest power you need. Most professionals begin using loupes with a magnification power of 2.5X. Remember, as the magnification increases, the field of view, focal range and light transmission decreases. Step 2: Choose working distance. All loupes are pre-set to focus at a certain distance and objects will remain in focus within a range of several inches. Loupes are available in 4 working distances: Short (10-13"), regular (12-16"), long (14-18") and extra long (16-20"). The 350 Series (3.5x) is the highest magnification optic available in a compound lens design. The 350 series optic is an excellent choice for dentists and surgeons requiring high magnification in a lightweight loupe. Kit contains: head strap, screwdriver, storage case, cleaning cloth, solution, magnification loupe and frame.