1 First, choose the lens of the jewelry magnifying glass, and the aperture of the magnifying glass is 18mm.

2. Secondly, when observing a plane through the lens, the center and edge should be equally clear; When observing a straight line, the thickness of the edge and the center should be the same.

3. Finally, when observing black characters on a white background through the lens, there should be no yellow or blue halo at the edge of the black characters.