Songzi Optics 4X Sport Frame Kepler Binocular Medical Surgical Loupes with LED Headlight for Dental Brain Surgery,Vascular Anastomosis Operation,Others (Working Distance: R(420mm)) Sport frame loupes can't wear over eyeglasses. If customer wear eyeglasses, we recommend you to choose headband loupes which can wear over your glasses.Please find these model loupes in Songzi Optics Store. LED headlight High intensity:1500030000Lux, Continuous run-time:4 hours.LED headlight High intensity;1500030000Lux,Operating Time:4 hours,Light head weight: 9g,---Battery pack weight:100g,--- LED bulb:1 W,---Charge voltage:AC110V/240V/50-60Hz. Magnification:4X , Material: optical lens ,Certificate: ISO9001:2008,CE. 4 kinds of working distance: S(340mm), R(420mm), L(500mm), XL(550mm). 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 patient's : this is you working distanc Choose the distance that is closest to the selection we offer.IF you are a dentist , your height is in the range from 160cm to 180CM,we recommend regular (420mm) working distance.IF you're a surgeon, you are sitting while working, your height is from 160cm to180cm, we recommend working distance R (420mm ). IF you are standing while working, your height is from 170cm to 180cm, we recommend L (500mm) working distance, even XL(550mm) working distance will fit for you.