If you are a beginner who want to use loupes , we suggest you to choose magnification 2.5X, because lower magnification loupes have bigger field of view, so loupes focus easy. The pupillary distance can be adjusted by one center axis,it is very simple and convenient for user. 4 kinds of working distance : S(280 - 380 mm), R(360 - 460 mm), L(440 - 540 mm), XL(500 - 600 mm).Please choose your working distance when you place order. If customer wear eyeglasses, we suggest you to choose our titanium frame loupes which can be mounted Prescription lens (RX lens ). Loupes Material: optical lens.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 is fit for you.Please choose your working distance. Each Loupe Set is complete with locking lanyard, microfiber lens cleaning cloth, screwdriver and padded case.