Thanks for the tip on selecting correct diopter strength. The more I look at them the more appealing they become. At the risk of sounding stupid, how do I find out what distance my lens focuses down to?
If it has a conventional distance scale, just read it there. If it doesn´t, just set it to manual focus, turn the ring until you´re sure you´re at the near end, look in the VF or LCD and move the outfit back and forward until, say, a row of books looks sharp. Then measure the distance between the camera and the subject; that´s it (it doesn´t have to be super accurate for this purpose).
Can you combine an achromat with a tube?
Yes, you can. Only, the achromat doesn´t add very much magnification over a typical set of tubes, so it´s hardly worth the trouble...
I just came across teleconverters. Are these used for macro too or are they what they sound, converters for lenses to make them telescopic?
You get the same close focussing limit with double the focal lenghth (for a 2x converter), so you do get about double the magnification. If you use tubes as well, put them between the converter and the lens, not between the converter and the camera body. However, converters often degrade the image noticeably.
