How much magnification required to see stylus?

You can get inner groove distortion from a dirty stylus. You can check for gunk buildup on a stylus with an 8x loupe. I do and it works.

Then I clean the stylus with a Magic Eraser, brush away the residue, use the loupe to ensure that the stylus is clean and play the cartridge again. If the distortion goes away it was a dirty stylus. If the distortion remains and your alignment is good, it's probably time for another stylus.

Attached is a link to a YouTube video showing examples and explaining cartridge wear. http://m.youtube.com/#/watch?v=iEVuP6-zYLE&feature=plcp

The reason for the question is that I was thinking of buying an USB microscope, they go for around 50$ on amazon. I was wondering if these would be sufficient for this purpose. 800x should do it.

Has somebody tried this.

I think a scanning Electron Micograph might tell you if it were worn. The problem is that using the stylus for the EM pictures destroys the stylus. If you could get certain wear states to correspond to a typical sound like Elizabeths inner groove distortion a series of worn scanning electron micographs vs nomal unworn styli would be useful.

Elizabeth is correct. To judge wear, you need at least 200X and up to 500X is helpful for micro types. You also need high intensity lamps on either side of the stylus. Then you have to know what you're looking for and how to judge.

The professional Audio Technica scope was 100, 300, 500X.
The later Shure scope was 200X.
Regards,

IMHO, 15X magnification is the minimum, higher will be better.