In article ,
Bob Engelhardt wrote:

Harold and Susan Vordos wrote:
...
I have a few pairs of 3.25 diopters. For close-up work, I'd love to have
some even higher, but I've yet to find them. ...

It may be at higher diopters the depth of field is so small that they
aren't very usable.
Bob

I frequently buy 4.00 and once in a great while up to 4.5 from flea
market vendors. Last Sunday I bought some 4.00

Chuck P.