Magnifying light with higher power are usually reserved for close-up inspection and measurement... 3 diopter = 1.75 times magnification, 13" focal length 5 diopter = 2.25 times magnification, 8" focal length 7 diopter = 2.75 times magnification, 5.5" Focal length is a general rule of thumb. As your magnification increases, your lens and focus will become smaller.
One of the main advantages of a magnifying light is the ability to handle objects with both hands while zooming in. Hands-free operation is absolutely essential when repairing electronic equipment or other close-up work.
1. Use eyes when using the magnifying light, just like using a pair of comfortable prescription glasses.
2. Make sure the lens is positioned to keep your subject in focus, 8 to 10 inches from the glass. This will give you the best magnification and minimal distortion.
3. For best results, keep the height of the chair and the position of the work surface to maintain a good posture. When viewing objects, keep away from the lens.