I use a B&L 7x APO Triplet, by far and away the best lens for under $75.00 IMO. Zeiss would probably be a touch better, I don't think for general coin viewing or grading you would ever need more than a 10x power, for variety hunting, 15-30x can sure come in handy, I have a really old Panasonic pocket microscope that I think is 20x range and lighted, very nice for checking double dies and RPMs or RPDs.
"Buy the Book Before You Buy the Coin" - Aaron R. Feldman - "And read it" - Me 2013!
ANA Life Member #3288 in good standing since 1981, ANS, Early American Coppers Member (EAC), Colonial Coin Collectors Club member (C4), Conder Token Collector Club member (CTCC), Civil War Token Society (CWTS) member, Liberty Seated Collectors Club (LSCC) & Numismatic Bibliomania Society member (NBS), USMex, Member in good standing, 2¢ variety collector.
See my want page:
http://goccf.com/t/140440