3.5X Fire-New Clip on CH350 Binocular Dental Loupes Surgical Loupes magnification:3.5X, 4 kind of working distance : S(280 - 380 mm), R(360 - 460 mm), L(440 - 540 mm), XL(500 - 600 mm).The working distance is the distance between your eyes and the patient's body. It depends on the human height. If your height is less than 180cm,you should pick the working distance R(360 - 460 mm),If your height is more than 180cm,you should pick the working distance L(440 - 540 mm), Please choose and send email to tell us your working distance while you are ordering loupes. Color: Silver-gray ,Frame: TP sport frame, Material: optical lens , Field Of View: 60-65mm, Viewing Angle: 20-150 Depth of field: 100mm ,Weight: 47g,Certificate: ISO9001:2008,CE How To Choose Your Loupes: Determine your working distance, which will also automatically determine your field of view. While working on a friend or family member have someone measure the distance from your eyes to your patients : this is you working distance. Choose the distance that is closest to the selection we offer