Magnification in 2X, 3.5X, and 4 X Strengths - A 3.5x and 4X magnification surgical loupe reveals incredible detail but comes with a small field of view (30MM.) Your working distance has to be maintained more accurately, too. Choose a 4X loupe if you want to focus on a narrow work area and need to see the details that a higher magnification affords. A lower 2.5X magnification results in wider field of view (50MM) and lets you monitor a broader work area. Because of their greater depth of field, 2.5X surgical loupes allow more freedom of movement as they are less sensitive to changes in your working distance. Working Distance - Working distance is the approximate distance between your eyes and the object you work on. To choose a pair of surgical loupes with the right working distance, imitate the circumstances of a surgical procedure and try measuring your working distance. Keep your back straight and be in a comfortable working position. People below 5'7" height usually need loupes with 340 mm working distance while taller persons need ones with 420 mm working distance in a sitting position. Illumination - Vision can never be perfect without proper lighting. In case your work area is hard to light up, use our super bright LED light that attaches to our surgical loupes. There are two intensity levels and the power is adjustable at each level. You will find it hard to look into the illuminated area at maximum power setting. The battery can run for 7 hours continuously at the lower level or for 4 hours at the high level. The light weighs only 11 g and it illuminates a spot with a 70 mm diameter from 400 mm with 6000 K (pure white) color.