A nib is a 0.3 mm gap between two pieces of steel and almost every problem a pen has is visible in it: a misaligned tine, a bent shoulder, a hair in the slit, a baby’s-bottom grind that will not start. You cannot see any of that with the naked eye and you can see all of it at ten times.
This is an achromatic triplet — three elements, two glasses — which is the minimum that gives a flat field with no colour fringing at the edge. A cheap single-lens loupe at the same magnification shows a sharp centre and a smeared rim, which is exactly the part of the nib you are trying to look at.
The barrel is blackened brass, 28 mm, with a folding guard in walnut that protects the glass and makes a handle when open. Field of view 22 mm, working distance 25 mm. It will also read a watermark and a paper’s laid lines, which is a better use of it than you would think.
