There is also varying quality among close-up (diopter) lenses. The vast majority are single elements. Some are achromats (doublets) and perform to a higher standard. The Nikon 3T and 4T (in 52mm) and 5T and 6T (in 62mm) are designed for use with lenses with focal lengths between 80mm and 200mm. 3T and 5T are +1.5 diopter. 4T and 6T are +3 diopter.

Leica makes a number of close-up lenses which are well corrected doublets and designed for specific focal length ranges. You can probably find a chart for them online. They are called Elpro and came in older roman numeral designations, and newer arabic number designations in 55mm mounts. I don't have all the info on these. Elpro 1 and 2 are for 50mm lenses, Elpro 3 for 90-200mm lenses, and Elpro 4 for 100-200mm lenses. Leitz recommends stopping down to at least f:5.6 for higher quality.

I think that some of the better filter makers and camera makers also made doublet diopters, but don't have specific info. The doublets are usually thicker and have a noticeably wider edge on the mounting ring.

Lee