Thanks for your comments and the suggestions about options for higher than 1-2x photography. I know about them, and also have other more suitable lenses myself (just not at hand in the summer cottage). I first made a try with the Micro-Nikkor 105/2.8 AFS and the TC-20E resulting in 2x magnification. The result was pretty bad. I then tried the 85mm/1.8 Z which was much better, but not really excellent, as Birna points out.
I find the Novoflex Castel-M with presets for 2x, 3x, 4x, and 5x magnification very useful and precise, if you do not want to use an electronic rail.