Songzi Optics (2.5X,3X,3.5X Optional) Black Goggles Frame Binocular Medical Dental Loupes Surgical Loupes & High Brightness Headlight (Working Distance :(360-460 mm) R, Magnification:3.5X) LED headlight High intensity:15000-30000Lux, Continuous run-time:4 hours,Battery pack weight:100g, LED bulb:1 W,Charge voltage:AC110V/240V/50-60Hz. .2.5X loupes specification:Field Of View: 100-110mm,Viewing Angle: 20-150,epth of field: 100mm ,Weight: 57g 3X loupes specification:Field Of View: 75-85mm. Viewing Angle: 20-150,Depth of field:90mm ,Weight: 57g. 3.5X loupes specification:Field Of View:60-65mm. Viewing Angle: 20-150.Depth of field: 80mm 4 kinds of working distance : S(280 - 380 mm), R(360 - 460 mm), L(440 - 540 mm), XL(500 - 600 mm).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 distance. 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 (360-460mm) working distance.IF you're a surgeon, you are sitting while working, your height is from 160cm to180cm, we recommend working distance R (360-460mm ). IF you are standing while working, your height is from 170cm to 180cm, we recommend L (440-540mm) working distance, even XL(500-600mm) working distance will be OK.